Klitschko, who announced his retirement from the sport on Thursday after years as the top heavyweight boxer in the world, went on to declare Joshua the leader of the next generation in an emotional tweet.
Klitschko, who also won the super-heavyweight gold medal at the Atlanta Olympics in 1996, and his elder brother Vitali, who held the WBO and WBC titles, dominated heavyweight boxing for almost 15 years.
The pair were expected to meet in a mandatory rematch on 11 November in Las Vegas, with an announcement due next week, but the decision thwarts any hope of a repeat.
"As an amateur and a professional boxer, I have achieved everything I dreamed of, and now I want to start my second career after sports", Klitschko said in a statement released by his management.
Klitschko, 41, announced that he retires from boxing on August 3 via a video on his official website.
"I deliberately took a few weeks to make my decision, to make sure I had enough distance from the fight at Wembley Stadium", Klitschko said.
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"I never thought I'd have such a long and successful sporting career, I thank you all from the bottom of my heart", he told his fans.
The two-time former champion, who held the unified title from 2006-2015 before losing to Joshua's fellow Briton Tyson Fury, ends his career with a record of 64 wins and five defeats. It was the best choice of a profession I could have made. The Pulev mandatory was called some time ago and we already have signed correspondence that if it's not Klitschko then Pulev must be next.
"Because of this choice, I have travelled the world, learnt new languages, created businesses, built intellectual properties, helped people in need".
"I'm still able to do all this because of the global appeal of the sport of boxing".
"Now it is my turn, I'm honestly doing this with respect for the new challenges and also with tremendous excitement, passion and dedication".
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