Charlie Sheen says that ex-wife Denise Richards asked him to be the biological father of the third child she wants to have. “There was a request for a donation. Without getting into it here … there is a specific document relating to this that I am going to reserve for a court.”

But Charlie — who is engaged to Brooke Mueller — won’t be making a visit to the sperm bank in the near future! “I would sooner, in exactly what I’m wearing, walk on the surface of the moon. Does that answer it?”

In the New York Post‘s Page Six column, Richards denied Sheen’s claim. “I don’t want another child right now. I have my hands full,” she said.

Sheen has also filed court papers to modify the custody arrangement of his two daughters with Richards. Sheen has petitioned for more time with Sam, 3 and Lola, 2, as well as the right to hire his own nanny for the girls, instead of using a caretaker employed by Richards.

“What I am doing is pursuing a relationship with my daughters that is unpolluted,” Sheen tells Entertainment Tonight‘s Mark Steines. The Two and a Half Men star also wants limited telephone contact with his ex, whom he claims calls his house frequently when the children are there. “When I’m here with the girls, I don’t need to be answering the phone 20 times a day,” Sheen says. “If there’s a problem, I’ll call.”