Uh-oh! Is Kristen Stewart making angry calls to Katy Perry about Robert Pattinson?

Rumours are flying that Katy Perry has been instrumental in Robert Pattinson and Kristen Stewart’s latest break-up.

The Twilight lovers have been in trouble since it came to light that Kristen had cheated on Rob with married movie director Rupert Sanders, but the pair had been trying to patch things up.

With stories spreading that Katy encouraged Rob to end things, the latest claim is that Kristen has given the pop singer a piece of her mind.

“Kristen called Katy to ask her straight out,” a source told Now.

“Katy was stunned and things got awkward.

“She said there was no way she was messing with Rob, but Kristen didn’t believe her.

“Katy got off the phone as soon as she could.”

So, is Katy trying to get her claws into Rob? A source assured Hollywoodlife.com that they’re just friends.

“They are not a couple,” the source said. “They are friends and it’s only that!”