Wladimir Klitschko says he is "excited" by Anthony Joshua's first world title fight against IBF heavyweight champion Charles Martin.
Joshua will challenge Martin for the IBF title at the O2 Arena in London on April 9, live on Sky Sports Box Office.
Klitschko previously held the IBF belt before it was ripped away in last November's points defeat to Tyson Fury, who himself was stripped by the organisation.
The Ukrainian is hoping to regain the remaining WBO and WBA belts in his rematch with Fury, but has offered words of support for Joshua.
Klitschko, who has previously described the 26-year-old as a future world champion, tweeted: "Bro, believe it or not, but I'm excited for you! Good luck and kick ass on April 9th!"
Joshua has spoken highly of the lessons he learned during sparring sessions with Klitschko and expressed his gratitude to the former champion.
"Appreciate this, even more motivation to put on a good show for the people! Hope you're good Champ," Joshua tweeted.
The former Olympic gold medallist could lift a world title in only his 16th fight if he defeats Martin.