At 34 years of age, eight months after the Thrilla in Manilla, Muhammad Ali fought Antonio Inoki in June 1976 as part of an exhibition swing through Asia. It's not included on his boxrec record, and it doesn't count in his win/loss totals whenever people make a reckoning of his career.
Even by Ali's remarkable career this is a stand-out moment of madness. That's because Inoki was a professional wrestler from Japan.
There's a bit of a debate about how much of the fight was supposed to be orchestrated and how much Ali knew about wrestling in Japan at the time.
One story goes that Ali assumed it was all for show until he caught Inoki practising a few days before the bout and was astounded at the violence being perpetrated on his opponent's sparring partner.
A summit was had and rules were changed, stripping the wrestler of most of his armoury, apart from kicks on the ground. Even so it turns out an expert at kicking repeatedly kicking you is profoundly painful.
They fought a full 15 rounds with the crowd baying for blood which was never quite properly spilled. One report has Inoki landing 64 kicks to a mere six punches from Ali who was bamboozled by Inoki's willingness to lie on the ground and attract Ali on only to repeatedly kick him behind the knee.
The judges scored the entire thing a draw and the crowd erupted into riots.
Ali collapsed in the lift writhing in agony from the leg kicks before fulfilling two more exhibition fights in Korea and the Philippines despite the pain throbbing in his leg.
The pain was from two clots which upon his return to LA the medical staff feared might necessitate the amputation of his leg.
Maybe Floyd Mayweather and Conor McGregor were originally trash talking for mutual publicity, but since Dana White put his offer of $25m each on the table there is finally actual money on the go.
If, at the height of Ali mania, he can risk it all for a dollars in Japan, what's to stop Mayweather doing a deal now?
Ali-Inoki was a bore because they wouldn't let Inoki fight. Let McGregor fight Mayweather in a cage. We'd all watch.