Lady Gaga's friends have warned that her new boyfriend will break her heart.

The 25-year-old singer has been dating 30-year-old Taylor Kinney since meeting him on the shoot for her music video 'You and I' but pals are worried 'The Vampire Diaries' actor will cause her heartbreak after his former girlfriend accused him of being a cheat.

A source told America's Star magazine: "All of her friends are telling her to watch her step - Taylor is bound to break her heart. It's only a matter of time before he finds someone else."

Taylor's ex Brittany Sackett - an estate agent from San Diego - has claimed she was still in a relationship with the actor when he first started dating Gaga, who split from her lover Luc Carl for the second time earlier this year.

Brittany said: "She was with my boyfriend, and I found out he was cheating on me."

The pop megastar wrote 'You and I' about her Luc and she recently admitted she gets emotional when she sings the song because it brings up memories from their relationship.

She explained: "There is not one song on any of my records that wasn't written by me, and I think when you write your own music you find ways to reinvent [the songs] emotionally through yourself and performance so that they are different every night and that song you know, sometimes it's about the guys and sometimes it's about the fans."