The retired Canadian ice hockey ace took to his Instagram Story timeline on Thursday, March 21 to share a photo of himself smiling, dressed in a blue suit and tie, as he waved a mini American flag.
"Big day I'm officially American (sic)," he captioned the snap, which appeared to have been taken in the courtroom where he recited the Oath of Allegiance to become a U.S. national.
The 38-year-old, who previously played for NHL teams the Ottawa Senators and the Nashville Predators, wed Carrie in 2010.
Mike's citizenship news gives the couple another reason to celebrate, following the birth of its second son, Jacob, in January. He is a little brother for Isaiah, who turned four last month.
The stars have continued to add to their growing family by recently purchasing a black-and-white horse named Bojangles, giving Mike a new hobby to get to grips with following his sporting retirement last May (2018).
Carrie showed off the new family member in a pair of pictures posted online on Tuesday, March 19, when she snapped Mike spending time with Bojangles in a field.
"Every cowboy needs a horse ... and a hat," she wrote, joking, "I'm still working with him on the Southern accent."
Fisher also debuted his furry friend online, admitting he's dreamed about owning a horse for years: "Ever since I was a kid I've always wanted horses. Today I got my first!" he shared.
Bojangles' arrival comes about two months after Carrie and Mike adopted a puppy named Zero, joining the family's other pooches, Ace and Penny.