Phelps marked the first birthday of his son Boomer on Friday with a throwback photo taken on the day the boy was born, Today reported.
Writing on Instagram, Phelps noted that Boomer’s birth was “the best thing” that ever happened to him.
It also gave him a crash course in fatherhood.
“Nobody can really prepare you for it, you're going through it and you're learning as you go," Phelps told Today Parents last month. "Watching (wife Nicole) as a parent, watching her as a mom, she's the best. She's always reading things and just trying to make sure that his life is the best that we can make it."
The family is planning an around-the-world theme for his birthday party, Today reported.
"It's wild to think that a year has passed," Phelps told Today. "Nicole and I will still look at each other like, 'We have a child! This is our child.' It's probably the best thing I've ever, ever been able to be a part of."
In case you’re wondering, Boomer is already learning how to swim.