The former House and O.C.star shared her happy news at the Golden Globe Awards 2014 over the weekend, where she stunned in a floor-length, figure-hugging green gown.
Olivia told E!'s Ryan Seacrest on the red carpet that she is expecting a baby boy and joked he was just as excited as her to be at the glitzy ceremony.
"He was kicking the whole time, going, 'Where are we?!'"
Olivia also suggested she's due in May by telling Ryan she remembers the date by repeating the phrase, "May the fourth be with you", which is used to reference Star Wars Day.
The brunette star is engaged to Saturday Night Live comedian Jason Sudeikis, who recently appeared alongside Jennifer Aniston in Meet The Millers.
Olivia, 29, walked the red carpet at the Beverly Hilton Hotel solo, turning plenty of heads in her emerald Gucci gown, which hugged her baby bump.
Poking fun at some of the reactions to her dress, Olivia tweeted: "Hahaaaa I just heard someone say I looked like a giant, walking pickle last night at the Globes. As a pickle enthusiast, I thank you."
More Golden Globes fashion in our gallery below:
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