UFC champ Daniel Cormier is keeping it all the way real when talking about Brock Lesnar -- telling TMZ Sports he's genuinely "disappointed" the guy pulled out of fight negotiations.
"I wanted to fight Brock," DC tells us ... "but you can only really worry about things that you can control. I can't control that he doesn't want to fight anymore. He's done."
Cormier says he appreciates the UFC and Lesnar for trying to make a deal -- but at the end of the day, Daniel thinks the WWE offered Lesnar too much money to stay out of the Octagon.