Michael Phelps is content with the size of his family swim team.

The 28-time Olympic medalist have a busy household with their four boys—Boomer, 8, Beckett, 6, Maverick, 4, and Nico, 5 months. So, they are not in any rush to welcome baby No. 5. 

"Oh, I think that's it," Phelps exclusively told E! News at the June 26 premiere of the docuseries Fueled By. "Nicole will tell you too. I think she said she wanted a girl for me, but we have Onyx."

That would be the family's Great Dane, who the couple introduced to fans on Instagram in March and who costars with the swimmer in the new docuseries, a joint project from Purina Pro Plan that details how nutrition factors into elite athletes’ lives with their dogs.

"Onyx is our girl, so we got everything," Phelps continued. "We got four boys, we got an awesome girl now."

And it’s for his family—human and dog alike—that has shaped his perspective on nutrition. After all, it means a lot to see all of their milestones.

"Fatherhood has been something that's been special just because growing up kind of without a dad,” Phelps, whose parents divorced when he was young, admitted, “being able to kind of always be around and see every single step has been a treat."

Naturally, having four kids can be a little hectic, and with three close in age, big feelings come with the territory. So Phelps, a longtime mental health advocate, and his wife use a tried and true tactic to calm the waters.

"Three boys eight, six, and four kind of get roughhousing and get into it—there are a lot of big emotions," he said. "So when they're going at each other, we pull them apart and you say, 'Lion breath.' And then they're able to talk through the things that they're experiencing in their stomach."

Phelps continued, "As a dad, that's really cool to see, because we're giving them a tool to be able to help them control their emotions and identify their emotions and I think that's something that I didn't learn until later in life. So some of those little small things are hopefully going to make an impact and change how they look at mental health in the future."

And his expertise in both swimming and compassionate parenting has earned him a nickname from his sons.

"My kids call me Aquaman because I'm able to take care of my physical and my mental health," Phelps revealed. "Throughout my journey that I've been on, I think that's been the biggest part that has allowed me to be the best version of myself."

—Reporting by Nikaline McCarley

Read on to see Phelps' sweetest family photos over the years...

In 2017, the 15-month-old was immersed in the family business at the Huggies Little Swimmers #trainingfor2032 event in New York put on by the Michael Phelps Foundation.

Who needs a golf cart when you can hitch a ride with mom, as 4-month-old Maverick did at a tournament in Scottsdale, Ariz., in January 2020.

Beckett enjoyed a shore thing with his mom in July 2020.

Boomer practiced his "hello, adoring fans" stroke during the Men's 400m individual medley on day one of the 2021 U.S. Olympic Team Swimming Trials in Omaha, Neb.

The Phelps crew sparkled in stars and stripes on the Fourth of July.

Disneyland is always more grand with grandparents in tow. Nicole called the October 2022 excursion "the best trip I've ever had."

Merry Christmas from all creatures great and small.

There was plenty of dad to go around, as the boys enjoyed a snuggle with their 6-foot-4 father.

The Phelps family may not win any synchronized swimming medals, but those golden smiles are priceless.

Who needs a pool when you've got a whole lake?

Boomer, Beckett and Maverick bond in front of the king of all lion statues during their 2023 summer trip to the San Diego Zoo.

No running allowed by the pool, but making faces by the jacuzzi is encouraged.

Cupcakes took the cake for Maverick's fourth birthday in September 2023.

In case you didn't know who they're related to...

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