The 51-year-old Jimmy Kimmel Live host stops by The Ellen DeGeneres Showon Monday and expresses his doubts about Underwood's sexual experience.
"Do you believe the Bachelor is a virgin?" Kimmel asks DeGeneres.
"Well, he says he is," DeGeneres replies.
"I know he does. I used to tell my mother that too. I think maybe that's the deal. Maybe he doesn't want his mom to know that he's been, you know," Kimmel quips. "If I were to announce, like, 'Hey, just want everyone to know I'm an adult virgin,' people would say, like, 'Yeah that makes sense. Yeah.' But you look at this guy and it's, like, there's no way he is. It's just impossible."
The conversation continues, with DeGeneres showing a shirtless picture of the 27-year-old Bachelor.
"I mean, look at him! That's not a virgin," Kimmel exclaims, before revealing Underwood declined completing a polygraph test.
"So, you think this whole thing is so that women are like, 'Oh, I'll teach you.' That kind of thing?" DeGeneres asks.
"Oh, I didn't even think about that angle," Kimmel says.
"You can't really be bad in bed if you're not compared to anyone. You know what I mean?" DeGeneres replies.
This isn't the first time Kimmel has questioned Underwood's virginity. When the former NFL player stopped by Jimmy Kimmel Liveearlier this month, the late-night host questioned Underwood about whether or not he made it to the fantasy suite while filming The Bachelor.
"I will say the fantasy suite was the most pivotal week of my journey," Underwood admitted of the week where the final three contestants have the option of sharing a room with the Bachelor star for the night.
"You did go to the fantasy suite?" Kimmel asked.
"Yes, I made it to that week," Underwood jokingly answered.
Filming has been over since mid-November, which led Kimmel to believe Underwood is a virgin no more. "We keep hearing that you're a virgin, but you've probably had sex 185 times by now," Kimmel estimated.
"I don't know," Underwood said while blushing. "I don't know what to say."
"Wouldn't that be something, if you didn't know?" Kimmel teased. "Plot twist!" Underwood agreed.
"You know, if you come out of this thing -- I mean people have been driving you nuts with this virgin thing -- if you come out of this thing and you're still a virgin you might as well just never have sex ever," Kimmel told him. "You might as well forget it all together."
"I mean, I feel like for the longest time what The Bachelor's been known for is the journey for love and I think they're trying to angle it somewhere else this season," Underwood quipped.
Watch the video below for ET's interview with Underwood: