There's no hiding it anymore!
The pair was returning to L.A. following a visit to his equally pregnant sister, Tausha Kutcher outside New Orleans.
In an amazing coincidence, Radar has also learned that Kutcher's twin brother, Michael, and his wife are also expecting!
"They knew Mila was pregnant in late February, but didn't want to steal Mike's wedding thunder or take the spotlight off Tausha's baby news by telling people then," a soure tells us exclusively.
"The only person who knew about Mila early was Ashton's mom."