Former unified heavyweight champion Wladimir Klitschko is backing his former foe turned friend, Anthony Joshua, to get revenge by winning his upcoming rematch with Andy Ruiz.

Back on June 1, Ruiz dropped Joshua four times before the contest was stopped in the seventh round - giving the Mexican heavyweight the WBA, WBO, IBF, IBO heavyweight titles at Madison Square Garden in New York City.

The rematch is scheduled to take place on December 7th, in Saudi Arabia.

Klitschko's last fight took place in April 2017, after he was stopped by Joshua in the eleventh round. Klitschko announced his retirement from boxing a few months later.

Prior their bout, Klitschko had used Joshua as a sparring partner in a past camp.

And since their bout, the two have become friends.

"I have been there, and I lost against guys that I shouldn't. I believe Anthony was surprised himself by what happened," Klitschko told BBC Sport.

"Anyone can fail, so now he is going to show the character, turn it round, and come back with a big win. I hope he is going to make it."

In the last few months, Klitschko has constantly been rumored to make a comeback.

At 43-years-old, Klitschko has refused to completely rule out a return.

The veteran has dropped hints, several times, on social media. But he's also rejected the idea of fighting again.

Will a comeback ever happen? Klitschko doesn't know for sure.

"Will I be back in the ring? I have still got it? Will I come back? I don't know. No-one knows," Klitschko said.

"I work out every morning and I lie to myself that I am going to be back in the ring and it is a sweet lie. I just enjoy myself and keep myself healthy. I don't want to speculate or put anything in the air."