Leonardo DiCaprio caught between his girlfriend and 'Titanic' costar Kate Winslet

Leonardo DiCaprio's close friendship with his Titanic co-star Kate Winslet is reportedly causing trouble in his relationship with girlfriend Vittoria Ceretti.

As per sources, Vittoria has grown frustrated with the influence of Kate over Leonardo's personal life. They told Radar Online, "Vittoria isn't accusing Kate and Leo of hooking up or anything, so it's not about that."

"What bothers her is having to share him with another woman. She complains that he values Kate's opinion more than hers."

"She says every time they hit a bump, he somehow ends up bringing up what Kate thinks or what Kate once told him. It drives her crazy because she feels like she is competing with this idealized version of Kate that Leo has built up over 25 years," the insider noted.

It is pertinent to mention that Kate Winslet and Leonardo DiCaprio have remained friends for nearly three decades after starring together in 1997 Titanic.

However, Leonardo's girlfriend Vittoria reportedly feels that she's competing with an "idealized version" of Kate that Leonardo has built up over time.

The source said, "She respects the friendship, but she also thinks Kate inserts herself way too much and Leo lets her."

Adding, "The way he jumps when Kate calls or texts drives Vittoria crazy."

"But when she points it out, Leo just gets defensive, and they end up fighting. Now Vittoria's threatening to give him an ultimatum. She's not going to play second fiddle to another woman, even if that woman is just a 'friend,'" the source said.