They are the best of buddies in the Singapore swim team, goofing around for wefies, and you can even say they are brothers from different parents.
And Teo Zhen Ren knows, intimately, the fierce competitive streak that lurks in Joseph Schooling despite his cherubic face.
The pair were rivals who used to race each other in their childhood but are now close buddies. Teo is an Arsenal fan while Schooling supports Chelsea. Teo went to Raffles Institution while Schooling went to Anglo-Chinese School (Independent).
Teo, 22, said: "We've played a lot of sports together - Fifa (a computer game), table soccer, pool, even bowling. He can't stand losing.
"He's never afraid as well. On the last par for golf, the last shot to win at pool, he always steps up.
"We always have friendly trashtalk with each other. When I broke the national record, I told him 'I broke the national record, you haven't'. I've also said to him, 'You're never going to win the Asian Games gold' and 'Phelps will definitely catch up to you'.
"Most athletes might start doubting themselves but it works with Joseph because he's not afraid and wants to prove people wrong.
"Most swimmers say they want to go to the Olympics; for him, it's always been about winning."
David Lim, one of Schooling's former coaches and a former Olympian, said: "It's as though he tasted the feeling of winning when young and he's addicted to that feeling."
Warren Seow, Schooling's former classmate at ACS (I), said: "He was competitive even during PE lessons. He would try to run faster and be at his best when we played games like soccer. It's hard to believe that same boy would win gold at the Olympics."
Lim believes that because Schooling has this addiction to winning, he is not done yet, saying: "After he's let it sink in, there are other things he could be eyeing. First, the world record, then (Tokyo) 2020. Now that he's Olympic champ, he'll swim the 100 fly. But another way of motivating himself is to increase his repertoire of events."