Lennox Lewis has hailed Vitali Klitschko's longevity as WBC heavyweight champion and backed the Ukrainian to continue to reign when he meets Odlanier Solis in Cologne on Saturday night.
Lewis retired at the age of 37 after beating Klitschko on cuts in their fight in Los Angeles in 2003, while Klitschko reversed his own retirement after a four-year gap and is fighting on into his 40th year.
Lewis said: "Vitali was one of the toughest opponents I ever faced. To adapt to his height and reach was a real challenge for me. He will have all the advantages against Solis.
"To come back from his lay-off like he did and win the title again is a tremendous accomplishment. To continue winning at his age and to still have the drive that he does is amazing."
Unbeaten Cuban Solis, a former multiple world amateur and Olympic champion, is expected to provide Klitschko's toughest test since he squared off with Lewis and gave the champion all the trouble he could handle.
And Lewis acknowledges the challenger is not without a shot.
"Solis has a tremendous history and he kind of reminds me of myself with all his different amateur accolades," added Lewis.
Lewis believes one of the reasons Klitschko continues to fight is his quest for the single career-defining fight that still eludes him - but refused to say whether that fight could involve David Haye.
Haye has signed a deal to fight one of the Klitschko brothers later this year but Lewis batted away the inevitable questions about his fellow Briton, insisting instead that it was Solis' turn to take the spotlight.
Lewis said: "Vitali is still looking for his big show. I had mine with Mike Tyson and he's still looking for his.
"He is still searching for that glory, some guy to stand up and say I'm the man to give him the challenge that he needs."