The incident occurred after the musician, who earlier this week was declared People's Sexiest Man Alive for 2019, showed an alternate clip of his music video for "All of Me", where Ellen DeGeneres had replaced his wife in the video.
After the footage was shown, Legend told the crowd, "Don't tell Chrissy guys, she'll be very, very jealous of Ellen," when the "Bring the Funny" star jumped out of a box by his chair and scared the singer.
As the crowd cheered Teigen said that was "the hardest thing I've ever done," before apologising for swearing.
"I didn't mean to swear, I'm so sorry. Should we do it again?" she joked, adding she's "so exhausted" after hiding in the box for "a long time."
Legend added that he didn't know his first guest would be his wife, as Teigen wondered if he could "hear me banging around the box".
"He's very unaware of anything around him," the supermodel laughed, with Legend joking that if she wanted to cheat on him she probably could, as she joked back, "Oh I have a million times."
"But I'm the Sexiest Man Alive, how could you possibly?" Legend said, as she teased, "Oh my God this has really gotten to you."
Teigen added the win was "well-deserved" and recalled a comment she read to her hubby, stating, "This just proves to you that it doesn't take good looks to be sexy."