10/02/2000 at 01:00 AM EDT
For director Bruce Paltrow, making the karaoke-themed comedy-drama Duets proved harder than hitting the high notes in Abba's "Dancing Queen." First he lost star Brad Pitt
, who was set to appear alongside then-fiancée (and Paltrow's daughter) Gwyneth, when the pair broke up in 1997. Then, just before beginning production last year (with Felicity's Scott Speedman replacing Pitt), the elder Paltrow was diagnosed with throat cancer. "I had radiation twice a day for 6½ weeks before I started to shoot," recalls Paltrow, 56. Admits Gwyneth, 27 (brother Jake, 24, is a director): "My biggest challenge was to be professional...and not a scared daughter."
Working together, however, proved no challenge at all. "She was unbelievable," declares her proud pop, who is now cancer free. "Anybody who takes money for directing Gwyneth is a thief."
Stealing the show was Gwyneth's singing voice, although Paltrow père—who has been married to Gwyneth's mom, actress Blythe Danner, 57, for 30 years—says he has always known about his daughter's vocal abilities. "When Gwynnie was a baby, she and Blythe would harmonize together," says Paltrow, who made his name as the executive producer of TV's St. Elsewhere. As for his own vocal talents, "I wasn't allowed to sing," he says, "because Blythe didn't want me to damage the children's ears."