Carrie Underwood Wishes 'Handsome Hunk' Mike Fisher a Happy Birthday: 'He's the Only Fish in the C for Me'

The 34-year-old singer is her husband's biggest fan.

Carrie Underwood only has eyes for her husband, Mike Fisher!

The 34-year-old singer took to Instagram on Monday to wish her hubby a happy 37th birthday --  and share an adorably corny joke.

WATCH: Carrie Underwood Is Super Fired Up for Her Husband To Play in the Stanley Cup Finals -- See Her Tweets!

"Happy birthday to this handsome hunk! I'll never forget the day he told me he was asked to wear the 'C.' I was so proud on that day and I'm even more proud now to see him play in the #StanleyCupFinals," she wrote alongside a photo of Fisher, holding up his captain's jersey for the Nashville Predators. "He's definitely the only FISH in the 'C' for me! ????????."

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Underwood is definitely Fisher's biggest fan. See her amazing reaction to finding out her husband was going to the Stanley Cup Finals in the video below.