Ashton Kutcher and Mila Kunis are now planning a wedding and babies, but their former That '70s Show co-stars are shocked because the two "despised each other," during the making of the sitcom, Breaking Celebrity News has learned.

"Everyone shakes their head over the romance," a longtime friend of Kutcher, 36, and Kunis, 30, said.

"Ashton and Mila were absolutely not friends during much of the making of That '70s Show. In fact, they couldn't stand working together."

Kunis played spoiled rich girl Jackie on the sitcom, who was romantically involved with Kutcher's airhead character Kelso. That '70s Show ran from 1998-2006.

But according to the source, "The two were never close on the set. Quite the opposite!"

However, after Kutcher's messy split from wife Demi Moore, 51, in 2011, in which the actor was accused of cheating on her with a younger woman, "Mila was the one who came forward to bury the hatchet," the source noted.