On April 28, 2006, Brock Lesnar appeared inside the ring after
the final match of K-1 Hero's Las Vegas and has since signed a deal
with the K-1/Hero's. He is currently training with Miletich
Fighting Systems under UFC legend Pat Miletich. Brock Lesnar
announced on 12 August 2006 in Las Vegas that he has joined the K-1
promotion and will have his first Mixed martial arts match in 2007.
Royce Gracie then announced that he will serve as Lesnar's
trainer.
From wikipeida.com
Besides you can find a few videos of him related to this topic