A former East German amateur boxer and coach, Sdunek had been working for the Universum boxing group in Hamburg since the mid-1990s, coaching the Ukrainian brothers to world titles before semi-retiring in 2009.
"Today we received the sad news that our friend and former coach Fritz Sdunek has passed away," the Klitschkos said in a statement.
"When we came to Germany, Fritz was the most important person to us. He always supported us and was the coach that made us world champions - we will forever be grateful.
"Fritz's death is a huge personal loss to us. In these hard times our thoughts and prayers are with his family," they added.
Sdunek, a highly respected boxing figure in Germany, remained coach of Vitali until the end of his boxing career when the older Klitschko turned to politics in his home country following his last bout and victory as WBC champion in 2012.
He also guided current champion Vladimir to the WBO crown in 2000.
(Reporting by Karolos Grohmann, editing by Ed Osmond)
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