WWE Champion Brock Lesnar and WWE NXT Superstar Matt Riddle were reportedly involved in a verbal backstage altercation before tonight's WWE Royal Rumble event, according to Pro Wrestling Sheet.

There aren't many details available on the incident as of this writing, but word is that the two Superstars passed each other while walking backstage and a tense encounter came out of that. One source noted that Lesnar saw Riddle and wanted him to know the reality of the situation between the two.

It was noted by multiple sources that the encounter between Lesnar and Riddle was real, and not something that is a part of the storylines. Apparently they both met for the first time at Minute Maid Park in Houston ahead of tonight's Rumble event.

Riddle has spoken out against Lesnar for several years during media interviews, making it clear that he wants to be the one that eventually retires The Beast. During an interview on NXT television last year, Riddle talked about why he wanted to retire Lesnar.

"Retiring Brock... it's no secret. That's been the goal since I started wrestling, since the very beginning," Riddle revealed. "I like to set goals that seem impossible. Only one person can retire Brock Lesnar, only one person can end his career, and that person's going to be me.

"I don't like how he does it, I don't like the respect that he shows, and I don't like the workrate that he puts out. That's just my personal opinion. I think he's capable of more. Maybe it doesn't work out for me, maybe it doesn't work out the first time, but I guarantee you I'm going to beat him and I'm gonna retire him."

Stay tuned for updates on the incident between Lesnar and Riddle.