"That 70s Show" star Ashton Kutcher's plan to help out a charity by competing on "Who Wants To Be A Millionaire" has been scotched by Fox, which airs Kutcher's sitcom.

Variety reports that ABC had agreed to postpone Kutcher's turn on "Millionaire" to a night on which it wouldn't compete with "That 70s Show," and Fox appeared ready to consent, even though "Millionaire's" celeb episodes are airing during the key sweeps period, which helps determine advertising rates.

But on Thursday, one day before the taping, Fox reneged and refused to allow Kutcher to appear on the show, Variety said.

The young actor, who also starred in the hit teen movie "Dude, Where's My Car?", had hoped to compete and win money for a University Of Iowa support centre for families of transplant patients -- Kutcher's brother underwent a heart transplant, Variety said.

To console the actor, Fox is donating $32,000 to the centre.

"Ashton is saddened he can't go on the show, but he respects his network's decision and is grateful they're giving $32,000 to the hospital and the families that need it," a representative for Kutcher told Variety.

--AllPop