"Good luck winning a fight with your wife when her name's tattooed on your butt cheek," he captioned the picture, prompting this reaction from Duff in the comments section: "Finest tiniest booty around #youstucknowboy."
It's unclear whether the tattoo was the result of a bet, a dare, or simply a butt-based declaration of marital bliss.
The couple wed in a low-key backyard ceremony, officiated by Duff's Younger co-star Molly Bernard, in LA in December last year.
They met in 2015, a year after Duff split from her first husband, Canadian ice hockey player Mike Comrie.
Duff revealed during an appearance on The Talk in 2017 that it hadn't exactly been smooth sailing for she and Koma, having split and reunited three times.
"It's going so great," Hilary gushed of their rekindled relationship. "I mean, this is the third time that we've dated … third time's a charm."
Let's hope so, or Koma could be in for a painful tattoo removal.
