Complex sentence: Now that Parks was a full-fledged star, Columbia kept him busy in elaborate productions (including a couple of costume epics) until he appeared in the sequel, "Jolson Sings Again" (1949), which was another huge box office hit.
Split into simpler sentences: Now that Parks was a full-fledged star, Columbia kept him busy in elaborate productions. He made "Jolson Sings Again" (1949), which was another huge box office hit.