Michael Phelps revealed why he proper lolled during the US anthem

If there's one thing we took from our primary school days, it's that you must show respect and maintain composure during the National Anthem… until the very last line when you can throw your head back and roar like a good thing about how great Ireland is.

And we're fairly certain that that's the case across the board.

So, when Michael Phelps, who won the 200-metre fly final on Tuesday, was seen guffawing during the US anthem at the presenting of medals in Rio, the public were only dying to know what had set the US swimmer off during a rendition of The Star-Spangled Banner.

And thankfully, he didn't keep his fans in suspense.

Phelps heard the "O" during the anthem pic.twitter.com/s11m18A2ni

— Jameson Cokas (@jameson2111) August 10, 2016

Speaking to NBC after being awarded his 20th gold medal, the 31-year-old athlete explained that it was the presence of his hometown mates in the crowd which had caused him to crack up at a certain point in the anthem.

"My boys from Baltimore were down on the other end, and back in Maryland, we all say “O!” for the Orioles during that part of the national anthem," he explained referring to the Baltimore baseball team.

"And all of the sudden I hear them roar “O!” and I knew exactly where it came from, and I just lost it because those guys came down from Baltimore and New York City to be here, and it’s just special to see those guys in the stands," he said.

His boys from Baltimore? Excuse us while we melt.