The veteran boxer and former rugby league star, self-proclaimed as the best athlete Australia has ever produced, is finally done.

At 43, the body which took him to NRL grand finals and boxing world titles simply can't keep up any more.

It was a reality Mundine was made brutally aware of when Jeff Horn - 13 years his junior - began the pair's fight at Suncorp Stadium with a shot to Mundine's body.

From that moment, any illusion that 'The Man' would pull off a shock upset was obliterated in front of the thousands watching in the stands.

Less than two minutes later it was over when a Horn left hook knocked Mundine out.

"I'm 43 - I'm not 23 - you know what I mean," Mundine said after the loss.

"If I was bit younger, bit fresher, maybe things might have been better but that's the way it goes man."

Pre-fight Mundine had hinted his career may continue if he beat Horn and opened the door to further big pay-days.

But no amount of money is going to get him back in the ring now, he says.

"Nah man, I'm done," he said.

"That's life man. You can't cry over it, it's meant to be and we've got to move on."

For all his athletic brilliance, Mundine's outspoken ways have often put him offside with Australia's public.

The veteran was booed as he walked into Suncorp and then cheered when he was floored by Horn.

Not that the public hate is something he is bothered by.

"All the trash I talked, in the end it's an entertainment business and I've got to try and get bums on seats," he said.

"Obviously a lot of people don't like it, so you're going to get detractors and lovers, supporters. It's part of the game and I'm glad I've really united something for these guys to earn some big dollars."

As to the future Mundine says he'll continue to campaign against injustice and to use his legacy and story to "uplift and help people" as well as spend some well-earned time with his children.

Australian Associated Press