While Grazer chose Segal, it was apparently Murphy who came up with the idea for his co-star: the platinum-selling singer turned actress Janet Jackson, who hasn’t appeared in a movie since Poetic Justice in 1993. But the hiatus didn’t bother Murphy. “I’ve known for years that she’s a good actress,” he says. “I remember watching her on TV in Good Times when she was just a little girl. Now, she’s a superstar - and a really talented woman.”

Teacher’s pet, Murphy with his sweetheart, Denise Gaines (Janet Jackson). But Sherman’s attempts to marry the love of his life are rudely interrupted by alter ego Buddy Love.

Grazer was the first to respond to the suggestion. “When the idea of Janet came about, we thought, ‘Oh my God, What Janet embodies is exactly what we need in this character’,” he says. “It was the perfect marriage from the get-go,” agrees Segal. “She’s so professional, always prepared and sweet as can be. And her smile just lights up the screen: everyone falls in love with her. When you look into her eyes as she stares at Sherman, all you see is love. It’s amazing. The romance between these two people is completely believable and wonderfully tender.”

Fans of the first film will recall that (like the 1956 Jerry Lewis movie on which it is based) The Nutty Professor is a comic variation on the Jekyll & Hyde story. Sherman Klump, a gentle, unassuming, overweight, vaguely dysfunctional college professor, develops a formula which transforms him into the supercool, sexually irresistible Buddy Love. Where the professor is mocked by his fellow men and spurned by the opposite sex, Buddy Love can turn the tables on the former and is literally pursued by the latter. But, when Sherman falls in love for real, Buddy threatens to spoil everything.

The story of Nutty Professor II: The Klumps - from an original screenplay by Steve Oedekerk (who co-wrote the first movie with Tom Shadyac), Barry W Blaustein and David Sheffield, reworked by American Pie creators Paul and Chris Weitz - is basically more of the same, but with a few neat changes and significant twists.

As the new movie starts, Sherman is about to get married - to Denise Gaines (Jackson), a colleague who is every inch his equal professionally but several dozen inches smaller in girth. All is going well: Sherman is happy; the Klumps are happy; Denise is happy... Then Buddy Love resurfaces. Worse still, he has his eyes on Sherman’s latest invention: a revolutionary serum that can reverse the ageing process. Clearly this is something with long-term benefits for mankind, even if there are still a few glitches to be sorted out (like the fact that it wears off at unpredictable moments). But, as far as Buddy is concerned, the serum has only one use: it will make him even more irresistible to the ladies than he already is.