"This is something they both wanted," one insider tells Us. "They are both so happy."
Kunis' pregnancy news comes nearly one month after a source confirmed on Feb. 27 that the Jupiter Ascending actress was engaged to Kutcher. The former That '70s Show costars and longtime friends first went public with their relationship in spring 2011. See pictures of Mila here.
Another source says Kutcher is "very happy" with the news of his fiancee's pregnancy, although he still remains resolutely private about his personal life. "Ashton has been very private and cut off more than he usually is," the insider tells Us. But, the Two and a Half Men star has been chatting with a longtime pal who is newly-familiar with fatherhood.
"He has been talking about kids with Danny Masterson," the source reveals. (As previously reported by Us, That '70s Show alum Masterson secretly welcomed a baby girl with his wife Bijou Phillips on Feb. 14.)
Kutcher, who was once married to Demi Moore, finalized his divorce from the Margin Call star last November. He shares no children with Moore, although Kutcher did grow close to the 51-year-old star's three daughters during their marriage.
"I know they are planning on being as quiet about their life together as possible," the insider adds of Kutcher and Kunis.
(E! News also reported the news of the star's pregnancy on Sunday.)