Complex sentence: David Jackson, who was cast as Gan, was known to David Maloney from his days as an actor and it was while watching Jackson at a performance at the Royal Court Theatre that Maloney and Vere Lorrimer spotted Jan Chappell, who would be cast as Cally.
Split into simpler sentences: David Jackson, who was cast as Gan, was known to David Maloney from his days as an actor. While watching Jackson at a performance at the Royal Court Theatre that Maloney and Vere Lorrimer spotted Jan Chappell, who would be cast as Cally.