Britain's Prince William has grown into a "man", says biographer Penny Junor.
The 31-year-old royal has nine-month-old son George with Duchess Catherine - who he married in 2010 when she was referred to as Kate Middleton - has matured since becoming a father according to the English writer.
She explained: "He has grown up and matured enormously since Prince George was born.
"He has become a man.
"It happens to so many people when they become parents.
"Suddenly the late nights and passion for nightclubs give way to a much greater interest in your baby's vocabulary and getting an early night.
"With that comes a whole change of mindset and we have seen that with William.
"He knows who he is and what he has to do and he has embraced that.
"He has left the Forces and he has now decided that his royal career is his primary focus."
Last month the Duke and Duchess of Cambridge embarked on a tour of Australia and New Zealand and it is believed this helped them "consolidate" their relationships with those countries and showcased what a close unit the couple were.
A palace source told the Sunday Daily Express newspaper: "What the tour showed, if we did not know it already, was how well the Duke and Duchess work together.
"For the Duke it was an opportunity to consolidate his relationship with those countries and the feeling was it could not have gone better.
"The Duke is now in his 30s so he was always going to cut a more mature figure.
"Times have changed."

Steven Moffat deliberately chooses "odd" looking Time Lords.
The 'Doctor Who' executive producer believes the beauty of the titular time-travelling Gallifreyan lies in his charm and intelligence, so unconventionally attractive actors like Matt Smith and Peter Capaldi are perfectly suited to the role.
He explained to Radio Times magazine: "There's something about Peter's demeanour, his eyes, his attitude - he's tremendously bright and that comes out on screen. When you choose a Doctor, you want somebody who is utterly compelling, attractive in a very odd way.
"None of the Doctors are conventionally attractive, but they're all arresting. Handsome men don't quite suit. Matt Smith's a young, good looking bloke from one angle but actually the strangest looking man from another.
"You need that oddity; you need somebody who is carved out of solid star, really. It really is built around the abilities, the charm and the magnetism of a succession of different actors."
Steven also seeks stars with an ageless quality about them and likes the combination of boyish behaviour and an air of wisdom that new Doctor Peter possesses.
He said: "I always thought Matt, while a very young man, had something of the demeanour of a much older man, whereas Peter is a man in his 50s but terribly boyish and young at times. I like the Doctors to have mixed messages about what age they are - you can't really pin them down."

'The Simpsons' and 'Family Guy' crossover episode will air later this year.
Homer Simpson will come face-to-face with Peter Griffin in an hour-long special titled 'The Simpsons Guy' in September on US channel FOX.
The special episode, featuring characters from both hit animated shows, will see the cartoon patriarchs battle over which fictional beer is better - 'Family Guy' brew of choice, Pawtucket, or Homer's favourite beer, Duff.
The other Simpson and Griffin family members will also hit it off when Peter, Lois and the gang take a trip to Springfield - the fictional town 'The Simpsons' is set in.
Lois Griffin and Marge Simpson will become fast friends, while Bart Simpson and the youngest of the Griffin clan, Stewie, will bond over their shared love of pranks.
The exciting crossover was first announced by FOX last year, who said the Griffins would be "greeted by a friendly stranger named Homer Simpson who welcomes his new 'albino' friends with open arms".
Both shows air on Sunday nights in the US and will be back for new seasons later this year.
'The Simpsons' continues its streak as one of TV's longest-running shows, entering its 26th season in September, while 'Family Guy' begins its thirteenth season.

Ben Shephard has criticised 'Good Morning Britain' viewers for focusing on Susanna Reid's legs.
The 39-year-old presenter, who hosts the new ITV morning show along with the former 'BBC Breakfast' star and ex Sky News anchors Charlotte Hawkins and Sean Fletcher, has spoken out against people's complaints that her famous pins were hidden behind a desk.
He said: "I find it extraordinary. It beggars belief people say that. She's an incredible journalist who has worked for 20-odd years in this industry and seemingly that is important? There is quite a lot more happening in the world."
Ben praised his new co-host as one of the best broadcasters he's ever worked with.
He said: "I have had the pleasure of working with some broadcasters and journalists over the years and without a doubt, in a short space of time, I have realised how brilliant Susanna is."
The former 'X Factor' host also addressed his new show's ratings, as they are currently pulling in an average of 600,000 viewers, half of the regular audience of 'BBC Breakfast'.
He told The Sun newspaper: "Any TV show is hard to get right. It is something that gets worked on for years and years and years.
"The X Factor now is not The X Factor I when I worked on it at the turn of the century.
"I did the first three series and it is a completely different animal now. These things will naturally develop and grow and become something different."

Conchita Wurst is tipped to appear on 'Celebrity Big Brother'.
The Eurovision Song Contest winner, who has become an overnight star following her victory in the singing competition on Saturday (10.05.14), could be in line for a spot on the next series of the Channel 5 reality show.
The bearded drag queen made headlines as she sealed a Eurovision victory for Austria, and it now looks as though she may join the likes of 'Benefits Street' star White Dee in the famous reality TV house.
A spokesperson for betting form Ladbrokes said: "The odds firmly suggest we'll be seeing more of Conchita and it looks like she'll be sexing up the next series. Her arrival in the house is sure to see ratings rocket."
The flamboyant star has received criticism from conservative politicians in European countries such as Russia - known for its anti-gay propaganda law - with one branding her Eurovision victory "the end of Europe".
Conchita, who sang 'Rise Like a Phoenix', dedicated her victory to equal rights.
She said: "This night is dedicated to everyone who believes in a future of peace and freedom. We are unity and we are unstoppable.
"I share the opinion that this was not a victory just for me but for the people who believe in a future that works without discrimination and is based on tolerance and respect. This transcends borders."

Caroline Aherne is battling with lung cancer.
The 'Royle Family' star, who played chain-smoking Denise Royle in the hit comedy, has been quietly recovering from treatment for the disease after previously fighting off both bladder and eye cancer.
Caroline, 50, has decided to go public with her secret illness in order to help raise £3.4 million to improve care for cancer patients in Manchester, where she was treated.
The actress-and-writer and her brother, Patrick, were both born with retinal cancer, leaving her near-blind in one eye. She later struggled with bladder cancer.
Caroline said: "I've had cancer and my brother's had cancer and we know how it affects people.
"We're lucky in Manchester to have some of the best bits of cancer care -- and the last thing I want to do is knock the fantastic work that goes on in this city.
"It's brilliant that all these big institutions want to make cancer care better for Manchester people, but even the best doctors, nurses and managers on earth aren't going to be able to understand what needs improving unless people affected by cancer in Manchester get involved and tell them what needs to change."
The 'Mrs Merton' star has now backed the Macmillan Cancer Improvement Partnership, which will seek to bring together doctors, hospitals, patients and the council to improve cancer care in Manchester.
She added: "There are too many stories about bad communication leading to patients waiting too long and feeling ignored and abandoned and that same bad communication is contributing to poor statistics on cancer.
"The partnership needs people like us to start explaining to all the institutions what needs changing so that these big, complex organisations can get together to make the improvements."

Katherine Jenkins has been left "heartbroken" by the death of her best friend.
The 33-year-old singer is mourning the loss of Polly Noble after she lost a seven-year battle against cervical cancer.
She posted a picture on twitter yesterday (12.05.14) of herself and her friend and wrote: "Heartbroken. Rest in Peace my darling friend."
And in another photo on her Instagram page, she added: "Heartbroken - Sleep now with the angels."
The pair became friends when they were both struggling singers in 2001, and Katherine was on tour when her pal called in 2005 to break the news she had cancer.
The classical star previously recalled: "She didn't look or sound ill - it was just unbelievable.
"And of course the word cancer frightens the life out of me because I had watched my father die of lung cancer when I was 15.
"But he had been nearly 70, and Polly was just 24. She was too young; she had too much to live for."
Polly underwent surgery, chemotherapy and radiotherapy and was eventually given the all clear for three years, but in 2010, she found a lump in her neck that turned out to be a secondary tumour.
Katherine previously said: "This time her oncologist told her that although she could have more treatment, the cancer was ultimately incurable.
"She called me from the hospital with the news. Neither of us cried. We were too stunned."

Ellen Page admits the support she has received since coming out has "blown her mind".
The 'X-Men: Days of Future Past' actress revealed she is gay at the Human Rights Campaign's Time to Thrive conference in February and admits she expected to be subjected to some "vicious" comments afterwards.
She said: "I've experienced basically nothing but support, it's actually really kind of blown my mind.
"I thought there would be a lot more viciousness."
The 27-year-old star admitted she was "afraid" to make the revelation because of the expected backlash, and she thinks it is "beautiful" so many people have had kind things to say.
She told 'Access Hollywood': "Maybe that's because you're afraid and for some reason you have this perspective, because of probably your own anxiety.
"So to me, that's been the most beautiful thing, because it's so indicative of the change that's happened and the growth that's happening.
"For me, it's been basically nothing but support."
Meanwhile, Ellen has promised fans won't be disappointed by the new 'X-Men' movie, in which she plays Kitty Pryde/ Shadowcat.
She said: "I loved it. I was totally blown away, totally on the edge of my seat and also, really moved, you know, I found it really emotional. So for me, it hit all the marks."

Jenny McCarthy and Donnie Wahlberg will marry later this year.
The 'View' host and the New Kids on the Block star got engaged last month, but won't be waiting too long to tie the knot, as she hopes to do so in New York "soon".
She added to E! News: "I will say fall of this year!"
The blonde beauty already knows who she wants to design her wedding dress - and it'll be more upmarket than what her bridesmaids will wear.
Asked who will design her dress, she said: "Gucci, yes. Gucci, maybe."
She then jokingly added: "[The bridesmaids will wear] Forever 21, for sure."
And the 41-year-old star will have plenty of company walking her down the aisle.
Explaining who will be bridesmaids, she said: "[My sisters], all the comedians on the 'Dirty, Sexy, Funny' tour and Donnie's sisters."
Donnie's family own a restaurant, Wahlburgers, in Boston so Jennie hopes his chef brother Paul will cater their reception.
She quipped: "Why not some Wahlburgers?"
Jenny has 11-year-old son Evan from her six-year marriage to John Mallory Asher, while Donnie has sons Xavier, 21, and Elijah, 12, with his ex-wife Kim Fey, who he was married to from 1999 to 2008.

Kimberley Walsh is going on her final holiday before her baby is born.
The former Girls Aloud singer is looking forward to spending quality time in New York with her long-term boyfriend Justin Scott ahead of the "madness" that will come when they welcome their first child into the world in the coming months.
She said: "I'm off to New York this week with Justin for our final city break before the baby's born.
"We really love visiting the Big Apple. I'm looking forward to wandering around the city and spending quality time with Justin alone before the madness starts.
"And I can't wait to eat the breakfasts - pancakes with maple syrup are my favourite!"
When she returns from her holiday, Kimberley plans to take yoga classes in the hope they will help her relax and ease her anxiety.
Writing in her column for Britain's OK! magazine, she wrote: "I'm going to give pregnancy yoga a whirl. I can see how it would help, I'd imagine you'd find some sort of calm if you've got used to the breathing and you can tune into that state of mind during the contractions.
"I'm not sure that'll be the case for me. I'm a worried and I find it hard to relax, but it's definitely worth a try."

Katie Price is reportedly terrified of going into premature labour following revelations her husband has been having an affair.
The 35-year-old star - who recently announced that she was six months pregnant with her fifth child - revealed on Twitter last week that her husband of just over a year, Kieran Hayler, had been having a "full blown sexual affair" with her former best friend Jane Pountney, and she's now said to be worried that the stress is going to cause her to go into early labour.
A friend of Katie's told the new issue of Now magazine: "Her stress levels and blood pressure are sky high. She was terrified she was going to lose this baby before all this stress. You can't imagine how worried she is about the effect this is all having on her unborn child."
The former glamour model, who gave birth to her and Kieran's first child Jett - now nine months old - two months early during an operation that took her and her son weeks to recover from, was advised to look after herself and her new baby by trying to avoid stress.
Another pal revealed: "Her doctor warned her before all of this that she had to take care of herself and keep her stress levels down. Goodness knows what this is doing to her blood pressure. We're all so worried about her."
Speaking about her shock pregnancy last week, Katie confessed that she had already experienced a scare, but that Kieran had helped her through it.
She said: "I felt these awful pains. That was terrifying because you know you don't know what's going to happen.
"[The doctor] knew immediately what was wrong - there were complications. All I thought was, 'Thank God Kieran's with me.' He was brilliant. The doctor explained what steps I would need to take to keep the baby and myself healthy. I was scared I might lose the baby."

Paul 'Bonehead' Arthurs claims Liam Gallagher would have told him if Oasis were reforming.
The 48-year-old guitarist reckons he'd be the first to know if the warring Gallagher brothers had put their feud behind them and were reforming the Brit Pop band.
Liam sparked speculation the band were getting back together when he took to Twitter to individually tweet a letter of the band's name every half an hour, sending the internet into meltdown.
The musician told The Sun newspaper: "Everyone hopes it happens, but there's nothing going on. I met Liam in the pub that evening he tweeted the letters spelling the band and he didn't mention he'd done it. Next thing, reunion talk everywhere."
However, Bonehead refused to rule out the possibility altogether, adding, "Never say never."
The mysterious posts came just two months after Oasis announced they are re-releasing their debut album 'Definitely Maybe' with previously unheard tracks to celebrate the LP's 20th anniversary on May 19.
The band split in August 2009 after Liam, 41, and his brother Noel, 46, had a huge backstage bust-up at a festival near Paris, France.
The pair were spotted avoiding each other this month at the Etihad Stadium, where they watched Manchester City win against West Ham to clinch the Premier League title.