The mothers of both stars were influential figures in the story, so Spacey has picked two award-winning actresses to portray them. Greta Scacchi has been chosen to play Dee's mother in the film that explores Darin's relationship with late Fifties teen star Dee.
Darin - the big heart-throb rocker of his day - will have Brenda Blethyn to play his ma.
The picture, called Beyond The Sea, after one of Darin's hits, features Spacey playing Darin and fellow American Kate Bosworth as Dee.
The cast, which also includes John Goodman, Bob Hoskins and hot young jazz performer Peter Cincotti, have been rehearsing in London with Spacey (who's also directing). Filming begins in two weeks, in Berlin.
Darin met Dee while she was working in Europe, so various Continental landmarks will be incorporated on German locations or recreated on film studio stages.
Rob Ashford, the choreographer from Thoroughly Modern Millie, has been putting the actors through their dance steps.
Ms Bosworth, by the way, has become familiar with London thanks to her British boyfriend, Lord Of The Rings star Orlando Bloom.
