Speaking to Entertainment Tonight during the 2018 iHeartRadio Music Festival at the T-Mobile Arena in Las Vegas on Saturday, Bryan shared that his gift comes from a hobby he shares with Underwood and her husband, Mike Fisher.
"Well I'm gonna send them some fishing rods," he said, noting that he thinks the couple will be having another boy.
The interview also marked the first time Bryan learned of Underwood's baby news, with the "Sunrise, Sunburn, Sunset" singer sharing his excitement for the pair.
"Oh that's news to me! That she's pregnant," he said. "I'm very, very happy for them!"
"That's so good, I'm so glad to hear that," Bryan added.
The American Idol judge also shared that he and Fisher have become good friends over the years now that they're both "Nashville guys."
"He has his the guy that built his lake, and my fish guy, we're all kinds of linked," Bryan said. "Mike's building a pond, I built a pond, that's our big connection… because we have little boys, and little boys have to have somewhere to go fishing."
Underwood and Fisher share 3-year-old son Isaiah while Bryan and wife Caroline are parents to sons Thomas, 10, and Tatum, 8.
During a recent appearance on The Ellen DeGeneres Show, Underwood revealed that she does know whether she is expecting a boy or girl, though she didn't share the news with host Ellen DeGeneres.
"We like to kind of just hold onto things for a minute," the "Love Wins" singer explained. "I feel like everybody just knows everything about everybody, so we just like to have a little secret for a little while."
"You can tell us in a few minutes," DeGeneres assured her. "Keep it to yourself for a few minutes and then let us know."
Despite Underwood's choice to keep her secret, DeGeneres did her best to guess whether the Oklahoma native is having a girl or a boy.
"I can probably tell you what it is. You have a little boy, right? How are you carrying versus when you carried him? Are you higher or lower?" she asked.
"It's a different ball game. I feel like I didn't look pregnant, and then I woke up and I looked like this!" Underwood responded. "I feel like you're trying to get me to talk about it so I'll say 'he' or 'she!'"
"No, I've got other ways," DeGeneres cracked before guessing, "It's a girl. It is."
"You think?" Underwood queried with a neutral expression. "OK. OK."
Photo Credit: Getty / Kevin Mazur0comments