London, Jan 22 : Dominic Cooper and Amanda Seyfried, who play on-screen sweethearts in the musical `Mamma Mia!' have broken up with their respective partners - because their reel-life romance turned real.

The couple, who play Sky and Sophie in the hit film, embarked on an affair while filming in Greece.

Rumours of a real-life romance between Cooper, 30, and Seyfried, 23, started making rounds after the pair was spotted together at a restaurant in Bath.

And now, Joanna Carolan, 30, Cooper''s girlfriend of 13 years, has spoken about the break up in an interview with Grazia magazine.