ANTHONY JOSHUA celebrated his win against Kubrat Pulev with Floyd Mayweather - who travelled to London in support.
Mayweather was a ringside guest for the thrilling fight with Joshua ended with a beautiful one-two combination in round nine.
The boxing royalty was heard cheering AJ on and encouraging the champion to utilise his jab.
Joshua scored four knockdowns on the way to closing out the show in devastating fashion, with Pulev laid out on the floor.
Before the headliner started, Mayweather gave the Brit star a rave review.
Mayweather told Sky Sports: "It's always good to see some great boxing.
"The UK is a great place, great fighters, I'm proud of Anthony Joshua but it's lights camera, actions.
"He's one of the best heavyweights, got a gold medal before, his careers going great, two-time word heavyweight champion, he's helluva' fighter.
"Anything can happen in this world of boxing. One shot can end your career.
"He's a great fighter, hell of a guy, gentleman and I respect his craft."
Most read in Boxing
The surprise appearance comes as Mayweather recently announced a 'special exhibition fight' with YouTuber Logan Paul.
Social media star Paul, who lost his pro debut to internet rival KSI by split-decision last year, will face the 43-year-old in February.
Mayweather retired as a pro in 2017, beating ex-UFC champion Conor McGregor in ten rounds.
But he did come out of retirement a year later in Japan to beat featherweight kickboxer Tenshin Nasukawa in one round.
Mayweather confirmed he will return to Tokyo next year, but first fights Paul - who will come into the farcical mismatch with a FOUR STONE advantage.