Lots of people were surprised when Jimmy Fallon and his wife Nancy became new parents recently, and it turns out that was partly by design. In fact, few people knew they were expecting -- because the couple used a surrogate and told almost no one.

Well, this would certainly explain why Nancy never looked pregnant.

"My wife and I had been trying a while to have a baby," Fallon told Savannah Guthrie during an Aug. 9 appearance on 'Today.' "We tried a bunch of things – so we had a surrogate."

“We said, ‘We’re not going to tell anybody,’” he explained. “It’d be just more fun if it’s just private between me and my wife. And then we get to introduce her to everybody."

Jimmy went back to work just one day after daughter Winnie Rose's birth on July 23, and during his monologue that night, the proud new papa told his 'Late Night' audience, “It’s very taxing on the fathers. I don’t know how it is for the mothers, but [it's] very taxing [for us]. I’m emotionally drained.”