AceShowbiz -

Mila Kunis and Ashton Kutcher have just revealed a dirty secret about them in the past. Stopping by "The Ellen DeGeneres Show", the couple admitted that they once hooked up on set while co-starring.

Mila and Ashton were joined by Kristen Bell and Dax Shepard on the show. The couples were asked to play a game called "Never Have We Ever". Each couple was given two paddles with the words "We Have" and "We Haven't" written on either side. Ellen DeGeneres then asked some questions which they should answer with the paddles.

The game became more exciting when Ellen asked a raunchy question. She asked whether they had ever hooked up on set, and both couples admitted that they had. They also revealed that they never visited a nude beach before.

Tension escalated when Ellen asked if either group had used handcuffs before. Kristen hinted that she had not, but Dax said he had. Surprised with her husband's answer, Kristen excalimed, "He's talking about another partner, Ellen." Dax then defended himself, saying, "No, no, no, no I'm talking about the police and stuff. Is that not what that means? That was a sexual thing. Normally all I think is sexual stuff, but this time I went legal."

At one point during their appearance, Mila and Ashton also revealed that they wanted more kids. They already have a daughter named Wyatt and they're now working on baby number two.