Joshua is leaving no stone unturned ahead of his rematch with IBF, IBO, WBA, WBO heavyweight champion Andy Ruiz – which takes place on Saturday night in Saudi Arabia.
Klitschko retired in 2017 at the age of 41, a few months after getting stopped in the eleventh round by Joshua before a crowd of 90,000 at Wembley Stadium.
After their fight, the two boxers became good friends and Joshua would often call him to get pointers ahead of tough fights.
The toughest test ahead for Joshua is the upcoming rematch with Ruiz, who dropped the British fighter four times to secure a seventh round stoppage in June.
“[Klitschko] said loads of stuff to me, Wlad was definitely ahead of the game. He’s more disciplined than me, he’s more diplomatic,” Joshua said.
“He was giving me dietary and training advice and that is maybe what people are talking about now when they see a difference in my body. Maybe that’s why – because I’ve adapted some of his teaching – my weight may fluctuate.”
Joshua is very motivated to reclaim his world titles, but says those four belts should not define him as a fighter.
“There’s nothing I’ve missed about being world champion,” Joshua said. “I’ve always said the belt should never define the man. I walked as a champion before I even had a belt.
“This is fighting. One loss doesn’t take the spots off a cheetah. We don’t play games when it comes to boxing, we’re serious and after I took the loss I’ve had time to reflect. I now have things to prove to myself. I want to take it more seriously because I’m going to that next level.”