However, ESPN's Ariel Helwani, who was interviewing Undertaker when the cameras caught the moment, helped clear the air with the Deadman on Wednesday (10:50 mark):
Apparently, there was no bad blood between Lesnar and the Undertaker, who was sent to the Honda Center in Anaheim, California, by the WWE:
"I was there to pick a fight. Yeah, I was sent there personally to pick a fight. I was unaware that [UFC President Dana White] had no clue what was going to happen, which I felt horrible about after the fact.
"I thought there had been some kind of discussion between him and [WWE CEO Vince McMahon], but at that time Brock was so hot in the MMA world.
"So obviously, you know what? Why not try it? There was no personal animosity, really, but it was basically me saying, 'All right, you left our world. I'm going to come into your world, and I'm gonna call you out,' and you know, that was it. And obviously it was a huge media storm, and it's all [Helwani's] fault."
Helwani then asked 'Taker to clarify whether he meant an MMA fight or something else.
"Like a wrestling fight. I was trying to get him back in my world. I'm pretty gutsy, but my days of getting into the Octagon are far past me. I mean, I am smart enough to realize that, but I thought if I could get somebody, obviously there was such a history there because of his run with WWE, and his success in UFC, this is huge if I could make it happen, so that was what it was all about."
Undertaker then said that Lesnar knew he was going to be at UFC 121 but that he wasn't sure how much he knew about his plans.
Lesnar lost the UFC heavyweight title that night to Cain Velasquez in the main event. He did end up coming back into Undertaker's world, though, and the two had three battles in the mid-2010s. Lesnar ended Undertaker's undefeated WrestleMania streak in 2014, but Undertaker got revenge at SummerSlam one year later. Lesnar then defeated Undertaker at Hell in a Cell in October 2015.
These days, the 55-year-old Undertaker is semi-retired from pro wrestling but fights a few times per year. He won his last bout against AJ Styles in a Boneyard match.
Lesnar dropped the WWE title to Drew McIntyre at WrestleMania 36, ending a six-month run with the belt.