Is Keira Knightley's romance with Rupert Friend on the rocks?

It seems Keira Knightley's romance with boyfriend Rupert Friend is in trouble.

The first hint of possible problems came last week when Friend arrived without Knightley at the London Coliseum gala production of English National Ballet's The Nutcracker.

"We all wondered where Keira was, because it was a magical show," the Daily Mail quoted a fellow guest as saying.

"But Rupert offered no explanation," the guest said.

And although Rupert looked happy enough that evening, friends fear that behind his smiles, all has not been entirely well with his live-in relationship with Keira, 25. Indeed, some are saying it could be all over between them.