Katy Perry and Taylor Swift are "very competitive."
The 'Roar' hitmaker, 29, reportedly instantly knew that the 24-year-old singer, who also once dated her ex-boyfriend John Mayer, was talking about her when she revealed this week that she has penned a new track, 'Bad Blood,' about another famous female popstar that she considers one of her "straight-up enemies" after the rival, who she did not name, tried to "sabotage" her entire 'Red' world tour.
A source close to Katy, who posted a mysterious message about an unnamed mean girl on Twitter, saying "Watch out for the Regina George in sheep's clothing," one day after Taylor's interview was published, told Us Weekly magazine: "Katy knows Taylor's song is about her, which is why she tweeted that."
The insider added: "[They can be] very competitive."
The duo were previously thought to have been amicable, but never became real friends.
In her interview, Taylor also suggested there was a "personal" element to the conflict and claimed the other singer "tried to sabotage an entire arena tour" by hiring her dancers.
She added: "And I'm surprisingly non-confrontational - you would not believe how much I hate conflict. So now I have to avoid her. It's awkward, and I don't like it."
But the source close to Katy said: "They were loyal to Katy when it came time to launch the 'Prism' tour. She didn't steal them. Taylor just employed them when they weren't working for Katy."
Many fans thought that the 'I Knew You Were Trouble' hitmaker was talking about Miley Cyrus in the interview, but a source close to the 'Wrecking Ball' singer said she "didn't steal [Taylor's] tour people. She's not the focus on the song."
But the pal admitted: "Miley is competitive with Taylor."

Chris Martin and Jennifer Lawrence acted "super cute" together in Beverly Hills on Monday night (08.09.14).
The couple, who started dating in late June, were spotted enjoying a dinner date at La Dolce Vita, where they appeared to be in great spirits.
A source told PEOPLE.com: "They were super cute together. They were laughing a lot and Jennifer was acting all goofy!"
The 'Hunger Games' beauty, 24, is the first person the Coldplay frontman, 37, has romanced since announcing he was "consciously uncoupling" from Gwyneth Paltrow, 41, in March after 10 years of marriage.
The Oscar-winning star, who previously dated British actor Nicholas Hoult, is rumoured to be preparing to go on tour with Chris and his bandmates later this year.
The 'Magic' hitmaker has been pulling out all the stops to woo the 'Silver Linings Playbook' star, including writing love songs about her.
An insider recently said: "He writes her songs and loves taking her to private romantic spots. Chris is sweeping Jen off her feet. That's his thing."
Jennifer initially told her friends that her relationship with Chris, who has daughter Apple, 10, and son Moses, eight, with Gwyneth, wasn't serious, but she has become increasingly attracted to him since watching him perform in the UK earlier this summer.
The insider explained: "Jen was blown away at his London show.
"His music is absolutely part of the attraction. The better she gets to know him, the more she likes him."

Katy Perry claims most of her former boyfriends were "threatened" by her success.
The 'This Is How We Do' hitmaker, who is dating music producer Diplo and was previously in relationships with John Mayer and Florence And The Machine guitarist Rob Ackroyd, says she has "less time for bulls**t" as she approaches her 30th birthday on October 25.
The singer told the October issue of Harper's Bazaar magazine: "A lot of times I've ended up with people who have been intimidated by me, unfortunately. They say they're not, but it comes out in the long run. They're threatened, or there's resentment because they don't know how to handle it."
She added: "As I'm heading into my 30s I have less time for bulls**t. I look for the same characteristics: a sense of humour, someone who makes me laugh off the charts, someone who is sensitive, someone who loves and understands music, and who is really smart."
But Katy, who split from ex-husband Russell Brand in December 2011 after 14-months of marriage, has learned a lot from her past relationships.
She said: "I had to learn about taking care of myself before I could take care of others. I want to mommy everyone. I want to take care of them. I want to save them, and I forget myself in the meantime. I learned that through therapy."
The brunette beauty wants to focus on her career instead of settling down, but feels pressure to start a family.
She said: "Why am I a baby machine? Why can't I be a mogul? I want to have a baby, sure, but I want to have a career. I want to have a record label. I want to have an incredible tour. So I'm going to have all of those things. Let's talk about that. It's like, get off my ovaries, okay? I'll do it in time."

Hilary Duff still really cares about Mike Comrie.
The 'Chasing the Sun' singer, who announced she had amicably separated from the former professional ice hockey player in January after three years of marriage, says they haven't filed for divorce because they are still working on their relationship.
The 26-year-old star, who has son Luca, two, with Mike, told KIIS 106.5's 'The Kyle & Jackie O Show' in Australia: "We've uncoupled, for now. I mean, if there wasn't a chance for getting back [together], I think we would've filed for divorce. We're not putting any... I talk about this so much, I really don't want to talk about it anymore. But we are like... I just talked to him this morning! We really care a lot about each other."
But the blonde beauty insists doesn't get upset by all the speculation about their marriage.
She said: "In my experience, there's truth to what's written. Usually, I find there's truth to a lot of the stuff somewhere."
Meanwhile, the former Disney star admits she was shocked that her ex-boyfriend Aaron Carter declared his love for her on Twitter in March.
Asked about the 'Crush On You' singer, whom she dated when she was just 13, Hilary told BuzzFeed: "I don't know how I feel. I mean, that was so long ago, and obviously I'm still married, and I have a baby and we kind of just... don't know each other. So, yeah..."

Chloe Grace Moretz loves that Brooklyn Beckham is really interesting and passionate.
The 17-year-old actress, who started dating the 15-year-old British heartthrob over the summer, says she is impressed by how serious he is about following in his famous father David Beckham's footsteps by becoming a professional footballer.
The 'If I Stay' star told the October issue of Teen Vogue magazine: "What I find really interesting about Brooklyn -- and what I really love about that kid -- is that he is passionate about what he wants, which is to be a pro soccer star."
She added: "He's very serious about it. And I enjoy someone who is on my level with the seriousness kind of thing."
A source previously revealed that David and wife Victoria Beckham are happy their eldest son is dating Chloe, but always make sure there is a chaperone present when they spend time together.
And the 'Kick-Ass' beauty admits her older brothers are equally protective.
She said: "My brothers will follow [my boyfriends] on Instagram and Twitter. It's a sort of [cyber warning] that says, 'I'm here. I'm on top of you.' "
The couple started dating three months after being introduced by mutual friends at Paris Fashion Week and were first spotted skateboarding together in Santa Monica, California in June.
An insider also previously revealed they enjoyed low-key dates at popular spinning gym Soul Cycle in Brentwood, Los Angeles over the summer.
The source said: "They cycle next to each other and are very cute. Always look to be cheering each other on with smiles. They also both seem very competitive, but in a fun way."

French Montana is trying to win Khloé Kardashian back.
The 29-year-old rapper was recently dumped by the 'Keeping Up with the Kardashians' beauty, but reportedly "won't really accept" their eight-month romance is over.
A source close to the 30-year-old reality TV star told E! News that the former couple are still in contact, as the Moroccan star is trying to save their relationship, "but eventually they will be totally broken up."
The source added: "For all intents and purposes, Khloé is single again.
"Khloé thinks he's a great guy but it just wasn't working out."
The fashion mogul ended her four-year marriage to Lamar Odom in December after months of rumours he cheated on her and was addicted to cocaine.
She quietly began dating the 'Pop That' hitmaker earlier this year, but decided to break things off because she grew weary of his "needy, obsessive" behaviour and slowly began distancing herself from him.
But Khloé's decision has nothing to do with rumours French was using her to boost his profile and sales of his latest album.
The insider said: "That stuff never bothered her because she doesn't care what people think. She's just decided to move on."
The duo spent a lot of time in the Hamptons, New York together over the summer and French is expected to frequently appear on her upcoming reality E! show, 'Kourtney and Khloé Take the Hamptons.'

David Beckham urged Prince William to "get some sleep" ahead of having a second child to look after.
The 39-year-old former footballer - who has sons Brooklyn, 15, Romeo, 12 and Cruz, nine, as well as three-year-old daughter Harper with his wife Victoria Beckham - dished out some friendly advice to the royal and his pregnant wife, Duchess Catherine, who is expecting the couple's second child.
When asked on ITV's morning show 'Lorraine' if he had any advice for William, David said: "Get some sleep because jumping from one child to two is a big step. Even though I thought jumping from two to three was bigger.
"But I'm so happy for them both because they're such great parents. To be great parents and have the roles that they have is incredible. I'm just happy they're going to have another one running around."
Clarence House confirmed the news on Monday (08.09.14) that Catherine is expecting a little brother or sister for the couple's 13-month-old son Prince George.
A message on the Twitter account for the royal household read: "The Duke and Duchess of Cambridge are very pleased to announce that The Duchess of Cambridge is expecting their second child."
Following the announcement, William and Catherine, who are both 32, might like to celebrate with a 'babymoon' at some of the pregnancy-friendly destinations as suggested by HouseTrip, one of the world's largest holiday home rental websites.
The site recommends a trip to Paris for the expecting couple, who could enjoy the views from the top of the Eiffel Tower or go shopping along the Champs Elysee.
Those suffering from morning sickness, such as Catherine - who is suffering from the same severe morning sickness she had while pregnant with George - don't have to worry about flying as babymooners can easily access the French capital via Eurostar. For more information, visit www.housetrip.com.

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