As they joined up at the center of the stage at the Bridgestone Arena in Nashville, Tennessee, on Wednesday, their cute, jokey monologue soon turned to her soon-to-arrive second baby.
Paisley -- who accidentally revealed the gender of Underwood's first child a few years ago -- didn't want to make the same mistake twice. So, he decided to bombard her with questions about it until she just snapped.
"Seriously, Carrie, gimme a little baby hint," Paisley said, before listing off a few pairs of classic male and female country duos. "Johnny or June? Keith or Nicole? Garth or Trisha? Tim or Faith?"
"No! I am hormonal, I will hurt you," Carrie shot back.
"Waylon or Willie?" Paisley asked, referring to Waylon Jennings or Willie Nelson, both male country icons.
"That doesn't even make sense!" Carrie shot back, as Paisley continued to pester her for an answer. "Oh my god! Willie! It's a willie!"
If it's not just a part of their comedy bit, it sounds like Underwood and husband Mike Fisher have another little boy on the way. The couple are already parents to 3-year-old son, Isaiah.
Paisley and Underwood's fun monologue, which also included some fun musical interludes, wasn't quite done poking fun at the singer's pregnancy. They later riffed on all the country stars who have been opening up their own bars and eateries in Nashville in recent years, and Paisley joked that, next year, "Carrie will be opening up her very own milk bar."
"For a very exclusive clientele," Underwood shot back with a laugh.
Before the show kicked off, ET's Nancy O'Dell spoke with Hillary Scott of Lady Antebellum, who predicted that Underwood would be making the big reveal during the show.
"I'm wondering if she's going to announce what she's having tonight, like maybe that'll be part of the monologue," Scott said, preciently. I need to know what baby gift to buy!"
Check out the video below for a look at Underwood's baby bump, which was on full display at this year's CMA Awards.