The boxing icons spent years linked to one another as fans debated a potential fight between them, with that question ultimately answered in 2015.
Mayweather outboxed Pacquiao and beat him by unanimous decision when their bout finally happened.
There was respect between them afterwards, but this did not fully end their rivalry.
Fast forward several years and the pair are both now retired from professional boxing.
Last year, Mayweather travelled to Japan for an exhibition contest against MMA fighter Mikuru Asakura, only for the organisers to bring Pacquiao out to promote the event also.
He attended the press conference prior the contest and sat next to Mayweather, prompting a remarkable exchange.
It began when Pacquiao arrived and announced: “I’m here to support my boxer, Asakura.”
Mayweather gestured towards his old rival and said: “There’s no blueprint on how to beat Floyd Mayweather, he can tell you that himself.
“When we talk about Hall-of-Famer, he’s a Hall-of-Famer, but nobody has the blueprint on how to beat Floyd Mayweather.”
There had also been rumours that the exhibition organisers were hoping to arrange a rematch between the pair.
So Mayweather told Pacquiao: “Don’t let them trick you into getting your ass whooped again.”
Pacquiao was more mild-mannered in his response, but still got a few digs in.
“He’s older than me, I’m still young,” the Filipino icon said, before boasting of his accomplishments that his rival didn’t match.
“What I have done and accomplished in boxing is one of a kind, because to get eight different weight divisions is not that easy.
“I’m not trying to boast what I have accomplished in life, but I am just saying this to repeat in case you forget.”
In an incredibly unsubtle shot, Pacquiao added: “The best fighter in the world has humility.”
Mayweather did not heed this humility advice as he fired back: “When we talk about what’s going on inside that squared circle, I’m the best, no matter how you cut it or slice it.
“No matter if you go one hundred years back or three hundred years back all the way to now, there’s only one best and that’s Floyd Mayweather.”