Katy Perry, a longtime friend of Pattinson's, "played a role, as one of many reasons," in the split, a source told E! News.
Pattinson was spotted moving out of the home he shared with Stewart Sunday after spending their respective birthdays separately. Both attended the annual Met Gala on May 8, but while Stewart walked the red carpet alone, Perry and Pattinson were photographed together, and later seen together after the ball.
“Katy was Kristen’s friend first, but she gets on with Rob brilliantly," a source told Heat magazine. "It’s clear to everyone that Rob’s got a bit of a crush on Katy and she totally plays up to it. They wouldn’t act on it, but it still makes Kristen feel insecure.”
But if anyone was to blame for the 3-year relationship falling apart, it's Stewart, whose affair with "Snow White and the Huntsman" director Rupert Sanders last summer disrupted what appeared to be a solid relationship.
And if Perry and Pattinson do start dating, it shouldn't come as much of a surprise: Perry reportedly admitted she had been nursing some more-than-friends feelings too -- and "would love to date him" if he were ever single.
2014: The Year in Music [PHOTOS]