"I came on [three years ago] and I was pregnant and it went so well, and I said to my husband, 'I'm going on Fallon, you know what that means. Gotta get pregnant," Larter said, standing up and exposing her baby bump.
"Hey buddy, I can't wait to meet you. We're going to be friends," Jimmy Fallon told the actress' stomach.
"It's so exciting. It's such a scary time and I've been trying to hide it as much as you can, and when you're in the public eye it's really scary in the beginning," said Larter, who will next appear on the TNT drama Legends. "I was still shooting my spy drama ... I had to be a covert spy in real life, too, so I'm wearing blazers and push-up bras and everything you can do to distract because the bump is growing."
Larter married MacArthur, who is stars in the upcoming TBS series Angie Tribeca, in 2009. They welcomed their first child, Theodore Hayes, in 2010.
Watch Larter's full announcement below.