UFC President Dana White appeared on Fox Sports' UFC Tonight show earlier today to promote UFC 223 and was asked about The Beast returning to the Octagon.
"Yeah," Dana responded. "Brock Lesnar's coming back. I don't know when but yes he is."
Lesnar's current WWE contract expires after WrestleMania 34 on Sunday, where he will face Roman Reigns in the main event. There's been talk of WWE working on signing Lesnar to a new contract but that has not been confirmed.
Lesnar's last UFC fight came on July 9th, 2016 - a win over Mark Hunt. That win was later overturned to a no contest due to failed drug tests related to the fight. The former UFC Heavyweight Champion currently has a MMA record of 5 wins, 3 losses and 1 NC.
White is asked about Lesnar at around the 7 minute mark in the video below: