Turns out that was a baby bump.

Though Olivia Wilde nixed pregnancy rumors at the end of January -- claiming her bump was "all burger" -- the 32-year-old actress revealed on Monday that she and fiancé Jason Sudeikis, 40, are expecting baby No. 2.

"Matching baby bumps," she captioned a picture with son Otis Alexander, who turns two on Wednesday.

EXCLUSIVE: Jason Sudeikis Jokes About His Son Otis' Big Mother's Day Plans for Fiancée Olivia Wilde

Sudeikis and Wilde have been together since December 2011 and got engaged in January 2013. They welcomed their first child together, Otis, on April 20, 2014, and Wilde told ET that she feels like she "won the life lottery."

"I'm just everyday more grateful and realizing how I have completely won the life lottery," the Vinyl star said at the UNITE4:HUMANITY event. "It's just so clear to me at every stage of his growth, and my own growth as a mother."

As for when the couple will finally tie the knot, Sudeikis joked on a recent episode of Watch What Happens Live! that he and Wilde are waiting "until weed is legal in every state, gosh darn it!"

ET's Lauren Zima caught up with the Angry Birds actor over the weekend and asked how his fiancée reacted to the joke. Hear what he said exclusively to ET in the video below.