Daniel Cormier is stepping up his training to prepare for Jon Jones -- sparring with 2-time UFC heavyweight champ Cain Velasquez.
Clearly, D.C. was impressed with Cain -- calling him "the greatest fighter I've ever been locked in a cage with."
"This is no joke @officialcainvelasquez is by far the best guy I've ever gone with."
Cormier vs. Jones is all set for UFC 200 on July 9th -- and D.C. is adamant he's finally going to get his revenge.
"This fight will be different. Head in the sand and let's get ready to go! #13days #andstill#newfight #newresult."