An eye-witness has lifted the lid on what really happened in an infamous spar between Anthony Joshua and Daniel Dubois.

The pair face off at Wembley Stadium on September 21 in a hotly-anticipated bout which will see Dubois defend his IBF title against the two-time world champion.

And, during the course of the build-up to the fight, a well-publicised 2016 training session involving the duo has inevitably been brought up.

Promoter Frank Warren boasted back in 2017 that his new recruit had knocked AJ down at the GB Performance Institute in Sheffield, despite the darling of British boxing having just become IBF heavyweight champion after beating Charles Martin.

Now, old ground is being retreaded, with former professional boxer Anthony Fowler claiming he witnessed the spar, TalkSport reports.

Anthony Joshua and Daniel Dubois face off at Wembley Stadium on September 21

During build-up, a well-publicised 2016 training session involving the duo has been brought up (pictured with Frazer Clarke, centre) (credit: @dynamite_daniel_dubois – Instagram)

Dubois (pictured, in 2017) is rumoured to have knocked Joshua down in a spar in 2016

At the time Joshua was IBF World Heavyweight champion after defeating Charles Martin

‘They were just sparring normally. Dubois was really young so he wasn’t really trying to win the rounds.

‘He was very cagey sparring Joshua. Obviously, Joshua was the main man on the team so he was always quite wary, but he always punched really hard.

‘Joshua must have been a little clumsy sparring him and he got caught with a short left hook and Joshua’s legs completely went.

‘Dubois could have hit him again and put him to sleep but Dubois had a bit too much respect for him to finish him off.’

Fowler revealed that the champion then tried to start fighting the then 18-year-old but he was told to take a break by his trainer.

‘Obviously, everyone was stood there like “Wow” and Joshua went and jogged around the ring because his legs were like jelly and he was trying to get his legs back.

‘And everyone was going “Wait, wait, wait”. Joshua wanted to carry on but [trainer] Rob McCracken was like “Have a little break, get your legs back to normal, and then spar” and then they continued sparring.

‘He didn’t knock him out, he didn’t hit the floor but he was really, really hurt.

Now, old ground is being retreaded, with former professional boxer Anthony Fowler claiming he witnessed the spar

The pair both head into the huge bout in the middle of winning streaks

Dubois is on a two-fight winning streak after knocking out Filip Hrgović in June and doing the same to Jarrell Miller (pictured, centre) last December

Joshua (right) has won four bouts in a row after losing two consecutive fights to Oleksandr Usyk, most recently knocking out Francis Ngannou (on floor) inside two rounds

‘Joshua used to get the better of most of the sparring but Dubois nearly knocked him out with 18oz gloves and headguards so if he catches him with those 10oz gloves Joshua will be going to sleep.’

Dubois is on a two-fight winning streak after knocking out Filip Hrgović in June and doing the same to Jarrell Miller last December. His overall record is 21-2 with 20 wins by way of knockout.

Joshua, meanwhile, has had a glittering career since his spar with Dubois, boasting a record of 28-3. He has won four bouts in a row after losing two consecutive fights to Oleksandr Usyk, most recently knocking out former UFC star Francis Ngannou inside two rounds.