A source close to Olsen, who's been dating New York artist Nate Lowman since the beginning of the year, tells the mag, "Mary-Kate has been looking a lot rounder recently. It is good she has put on weight, because she previously suffered from anorexia, but a lot of people think she could actually be attempting to hide her pregnancy."

While Olsen and Lowman are the two most directly responsible for the possible child-to-be, there was another party who played a role in the alleged pregnancy—deceased actor Heath Ledger, who is believed to have inspired Mary-Kate to start a family before his death in January. Apparently Ledger told Olsen that becoming a father to daughter Matilda Rose was the most rewarding thing he had done.

"Mary-Kate really took Heath's words to heart," the source reveals. "She wanted the same kind of fulfilment in her life that Heath found in his after becoming a dad."

As far as raising a child with Lowman, the insider adds, "She is really happy with Nate and is very excited they will soon be starting their family together." 

Hopefully, Mary-Kate can avoid the kind of family tension she's experienced as a sibling in her role as a mother.