The 33-year-old model and television personality jumped out at Legend, 40, as he guest hosted Friday's episode of the talk show.
Teigen was hiding in the "coffee table" that Ellen DeGeneres has used to scare other guests on set. Legend yelped in surprise before helping his wife out of the small container.
"That was the hardest thing I've ever done," Teigen said. "Honestly, I'm so exhausted."
Teigen sat down with Legend for an interview, where she shared her reaction to the singer being named People's new Sexiest Man Alive.
"It's well deserved," Teigen said. "I did love that comment I read to you this morning. They were like, 'This just proves to you that it doesn't take good looks to be sexy.' But it was trying to be a compliment. It was for the both of us, it was like, 'Look at this couple...'"
"'They prove that even average-looking people can be sexy,'" Legend jokingly finished.
Legend had kicked off the show by serenading a woman from the audience.
Legend was named People's Sexiest Man Alive this week. He told the magazine he was "excited" but "scared" to receive the honor.
"I was excited, but I was a little scared at the same time because it's a lot of pressure," the singer said. "Everyone's going to be picking me apart to see if I'm sexy enough to hold this title. I'm [also] following Idris Elba, which is not fair and is not nice to me!"
Teigen and Legend married in September 2013 and are parents to two children, daughter Luna, 3, and son Miles, 18 months.