Brock Lesnar and The Undertaker have shared the ring in WWE several times before, but it seems like their rivalry may extend beyond the wrestling ring.

Brock Lesnar's first stint in WWE ended in 2004, and after a run in the NFL, 'The Beast' decided to get involved in the world of Mixed Martial Arts.

Lesnar ended up fighting in the UFC, and won heavyweight titles there, but his stint with Dana White's promotion didn't come without a few losses.

At UFC 121 in 2010, Brock Lesnar lost his heavyweight title to Cain Velasquez after a first-round TKO, but it was what happened after the first that really caught the attention of fans.

Mere moments after Brock Lesnar stepped out of the cage, he was confronted by fellow former WWE Champion, The Undertaker.

'Taker was being interviewed by Ariel Helwani cage-side after the fight had concluded, but stepped away from the camera to stare down Lesnar, saying "You wanna do it?" to 'The Beast'.

It seemed like a heated confrontation was about to ensue, as can be seen below, with Lesnar not exactly standing down from The Undertaker's glare.

Helwani asked 'Taker if he and Brock Lesnar 'were cool', but 'The Deadman' explained that the issues between the pair are "personal".

Undertaker explained that he and Lesnar have issues, having the following to say to Helwani:

“I’ve got background with Brock, but that just showed you something right there.”

12 years on from the confrontation, we now know what actually happened between the two wrestling legends that night.

Speaking in 2020, The Undertaker sat down for another interview with Ariel Helwani, where he explained that he was "there to pick a fight" at UFC 121.

'Taker actually said that he felt terrible that Dana White didn't know what was going to happen, but explained that he was sent to UFC to bring Brock Lesnar back to WWE.

“I was sent there personally to pick a fight. And I was unaware that Dana [White] had no clue what was going to happen, which I felt terrible about after. I was there to pick a wrestling fight, bring him back to our world.”

Undertaker noted that the situation worked out perfectly, because Brock Lesnar walked right by him, when he could have just walked another way.

“It worked out, we got really lucky that he walked by us because he could have gone another way. If you watch it back, my wife, she kind of nudged me like ‘here he comes’ and I don’t know if I would have even done the interview had I been in the right spot."

The Undertaker WWE

The Undertaker went on to explain that he wouldn't be able to work for the UFC, so the only way he'd be able to mix it up with Lesnar again would be in WWE.

Brock Lesnar knew that 'Taker, who was 46-years-old at the time, was going to be at Honda Center in California for the show.

“He [Lesnar] knew I was going to be there, I don’t know how much he knew about what I was going to do.

Undertaker's mission to bring Brock Lesnar back to WWE proved to be successful, as 18 months later, Brock Lesnar returned to WWE, the night after WrestleMania 28.

Lesnar and 'Taker ended up working together again in WWE, with Brock becoming the first man to beat The Undertaker at WrestleMania in 2014.

The Undertaker has spoken about his negative reaction to being told that Lesnar was going to beat him at the huge show, which you can read more about by clicking here.

Brock Lesnar will face Universal Champion Roman Reigns at WWE WrestleMania 38 this weekend in a 'Winner Takes All' title unification bout, while The Undertaker will be inducted into the WWE Hall of Fame.