"I have learned a lot of patience," Michael Phelps previously told PEOPLE about fatherhood

Michael Phelps had a big announcement for fans on Sunday: he’s going to be a dad again!

The retired competitive swimmer — who, with a total of 28 medals (13 of them gold), is the most successful and decorated Olympian of all time — and his wife Nicole Johnson Phelps revealed on Instagram that they are expecting their third child.

“No. 3 on the way!” Michael, 33, captioned a photo of sons Boomer Phelps, 2, and Beckett Phelps, 13 months on his account — the two boys sitting in a car adorned with gold balloons spelling out the word “baby.”

“Can’t wait to see the journey that this takes us on!!!” Michael added. “#luckyman.”

Nicole, 33, shared the same image on her account. “Oops we did it again 🧒🏼👦🏻👶🏻 I get to be a mama x3!!” she wrote, adding the hashtag, “#herewegoagain.”

Neither appeared to know the sex of their baby-to-be, Michael asking, “boy or girl?” in a hashtag on his post.

Want all the latest pregnancy and birth announcements, plus celebrity mom blogs? Click here to get those and more in the PEOPLE Parents newsletter.

The future parents-of-three — who wed in June 2016 — also shared outtake photos of Boomer and Beckett to the two Instagram accounts they run for the boys.“I asked mom for a new baby for Christmas last year and …. well my wish finally came true!!!” they wrote in Boomer’s post. “I wonder if I’m gonna have little brother or a little sister?” “I’m not sure what this means but I was just told I’m promoted to Big Brother!!” they teased in Beckett’s post.RELATED: Water Babies! Michael Phelps Makes a Splash with Sons Boomer and Beckett to Promote Water Safety

Muhammad Ali's Celebrity Fight Night XXIII - Red Carpet
Michael Phelps and Nicole Phelps
| Credit: Frazer Harrison/Getty

Last April, Michael chatted with PEOPLE about fatherhood, explaining that he still has a lot to learn about parenting.

“I have learned a lot of patience,” said Michael. “Being able to be at that point where we are able to teach and raise our two kids exactly how we want is a journey we are really looking forward to and is going to be super fun. But I believe we are really just getting started. We are looking forward to wherever this is going to take us. It’s been a great learning process. But I think the biggest thing is patience.”

“It is difficult, but you just figure it out and make it work,” he added. “That is what you do as parents. There is no manual on how to do it. You figure it out along the way.”

Michael also sang the praise of Nicole. “I love my wife for everything she does for me and our kids,” he said. “It has been really cool for us, as a couple, to go through that. Nicole and I have been through everything you can imagine publicly and privately and this is only going to help and grow and strengthen our relationship.”