Brad Paisley may have his hands full with his four-year-old son, Huck, especially since he has "discovered" girls, most particularly, Brad's three-time CMA Awards co-host.

"Huck has the biggest crush in the world on Carrie Underwood," Brad Paisley tells People. "He is obsessed with her, and he's only four."

Little Huck met the object of his affection for the first time when Carrie visited the studio at Brad's farm last week. It didn't take long for the younger Paisley to charm the blond beauty.

"He went out and got her roses -- we took him to Whole Foods and he picked them out himself -- and he wrote her a Valentine and dictated it to his mom," Brad recalls. "He said, 'I hope you have an incredible day and night. Love, Huck.' That's what he wanted to say to her."

While making her swoon with his thoughtful love note, Huck also wanted to demonstrate his manly side, so he put on a display of incredible strength. "We were all hanging out in the studio and out of the blue, he said, 'Carrie, watch!' And he pushed the pillows off of the couch with both arms and held them above his head, and he said, 'Look how strong I am!,'" the proud father recalls. "It was like, 'Wow, the instinct is there already!'

"He likes her and likes her music a lot -- in fact, one of the things he said that was really funny the other day before he met her was, 'I don't like girls,'" Brad continues. "And I said, 'What about Carrie?' And he was like, 'Oh, I like her music.'"

Brad and his wife, Kimberly Williams-Paisley, can look for more of this demonstrative boy behavior, as their second son, 22-month-old Jasper, finds out about this boy-girl dynamic.

In the meantime, Brad is wrapping up his H20 Frozen Over tour with stops in Orlando, Fla. tonight (February 24), and Columbus, Ga., on Friday, February 25, with the final stop in his adopted hometown of Nashville on Saturday, February 26.

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