Daniel Dubois made news in 2017 after rumours circulated that he had knocked Anthony Joshua out while sparring.
Dubois, an 18-year-old amateur, faced Joshua, the recently crowned IBF heavyweight champion who defeated Charles Martin in April 2016.
Warren claims Dubois knocked out Joshua in sparring when he was 18 years old.
The shocking revelation came to light after Frank Warren signed Dubois to Queensberry Promotions upon turning pro in 2017.
In an exclusive column with talkSPORT, Warren wrote: “I first heard about Dynamite when I was told an 18-year-old lad had knocked out Anthony Joshua.
“This was in 2016, the same year AJ became a heavyweight world champion. Dubois was a boy and he knocked out a man in Joshua – a six-foot-six man at that!”
Dubois ran with the story in the early years of his career, proudly exclaiming he had ‘put down’ AJ during his time with the GB Olympic squad.
But in the present day, Dubois is far more coy on the topic.
“That’s the past now, we’ll leave that in the past. But we can bring it up again [if I fight Joshua],” he told talkSPORT.com.
Asked if there was any truth to it, Dubois smiled and laughed menacingly.
‘Triple D’ is now just one fight away from facing the man he claims to have decked all those years ago.
Joshua has never responded to the Dubois sparring story.
Dubois faces Hrgovic on Saturday at the Kingdom Arena in Riyadh, Saudi Arabia live on DAZN
According to Saudi boxing chief Turki Alalshikh, the winner of Dubois’ upcoming clash with Filip Hrgovic on the unprecedented Queensberry vs Matchroom 5vs5 card this weekend is the frontrunner to box AJ next.
Joshua is set to headline Riyadh Season’s debut UK card at Wembley Stadium with the soon-to-be-vacated IBF world title expected to be on the line in the main event.
“It’s huge, massive for both,” Dubois added. “Two British fighters fighting like that would be history.
“Frank Warren, the best promoter in the world, would love that so I’ve got to go out there and do that.”
In the lead-up to the Hrgovic fight, similar sparring stories have emerged.
The Croatian puncher claims he hospitalised Dubois when they shared the ring together in London six years ago.
But the 26-year-old shut down Hrgovic’s story, by saying: “They were good hard spars for me and him, if he’s honest he will tell you that…
“He isn’t riling me up. He’s just another guy who thinks he is highly rated. But who has he fought?
“Who has he fought that is a tough young athletic contender like me? He hasn’t fought anyone like me. And you guys are going to see on Saturday.”