"Actually, this is something I haven't even mentioned to anyone, if we could just keep it between the three of us and you all," he joked with the studio audience. "But I'm actually expecting a baby in July with my husband."
Host James Corden threw his hands over his mouth in surprise as Charlie and the audience applauded.
After James asked the star if the baby was a boy or a girl, Jesse quipped, "A human."
"I'm very excited, but it feels like I'm 44 now. I'm like, 'Let's get this show going!' I mean, it's already tick tock," he added.
Jesse and Justin tied the knot in New York City in 2013 after dating for two years. Following their first anniversary together, Jesse announced the couple would like to start a family soon, and a rather large one at that.
"At least eight, minimum!" he told People at the time. "We are very excited to start a family. We don't have any sort of timeline right now. When you have to look for alternate means, there's a little more planning that has to go into that, so who knows. When we start the process it might still be a three-year ordeal. We'll see what happens!"
While chatting with James and Charlie, Jesse also dished on filming the final episodes of "Modern Family," the popular ABC sitcom that began in 2009.
"It's incredibly sad! Something that I've been doing for 11 years," lamented Jesse, adding, "It's like first through 11th grade when I was a kid. It seems like a lifetime. Now it's flown by."
As to how saying farewell to the cast and crew will be handled, Jesse revealed he may have to duck out because it may be too difficult to handle.
"I'm big with an Irish exit," Jesse shared. "I do not like long goodbyes, so maybe that's what I'll do. Just like after my last scene, I'll just leave the lot and just drive home. I feel like that's the only way I'll be able to manage this. It's really emotional."