Cormier (21-1) claimed UFC's heavyweight championship belt at UFC 226 on Saturday, as he knocked out Stipe Miocic with a short right hand in the opening round. The finish came at the 4:33 mark after Miocic -- the longest-reigning champion in UFC heavyweight history -- crumpled from the shot.
Already UFC's light heavyweight champion, Cormier becomes just the second fighter ever to hold titles in two weight classes simultaneously. The first was Conor McGregor, who accomplished the feat in late 2016.
Lesnar, a professional wrestling superstar and former UFC champion, was sitting cageside at the event and entered the Octagon after Cormier, a pro wrestling fan, called him up.
"There's a guy I've known for a long time," Cormier said. "He's a wrestler. He's an All-American. He's a former UFC champion. I never thought I would fight him -- but Brock Lesnar, get your ass in here!"
The two squared off for a moment before Lesnar shoved Cormier in the chest and stated, "DC, I'm coming for you, m-----f-----."
Lesnar, 40, hasn't fought in UFC since he defeated Mark Hunt by unanimous decision at UFC 200 in July 2016. That result was later changed to a no contest after it was revealed that Lesnar had failed multiple drug tests. He is currently still under suspension by the United States Anti-Doping Agency.
"We're definitely going to make that fight," White said of Cormier and Lesnar.
Cormier, a former Olympic wrestler, put an end to Miocic's historic reign of three consecutive title defenses. It was the most consecutive title defenses in UFC heavyweight history.
Miocic, of Cleveland, landed a handful of right hands in the fight, but Cormier's hand speed stood out. He reddened Miocic's face with punches, and the finishing sequence was reminiscent of combinations he threw the last time he fought at heavyweight, in 2013.
Cormier would have remained in the heavyweight division, but he elected to move down to light heavyweight because of his teammate, former UFC heavyweight champion Cain Velasquez.
"I was a heavyweight for a long time, and I left this division," Cormier said. "I never knew what I could become, but tonight, I got the answer. I'm a two-division champion, baby."