Vitali Klitschko insists he would spurn a multi-million pound payday to fight his brother if he beats reigning champion Lennox Lewis in Los Angeles on Saturday.
The 6ft 8in Ukrainian would come under enormous pressure to defend the World Boxing Council crown against Wladimir should he end Lewis' reign at the Staples Centre.
But the 31-year-old vowed: "I only have one brother and he is the gift of my life. I cannot fight against my brother." Wladimir, the former World Boxing Organisation champion who is acting as his older sibling's main sparring partner at the La Brea Boxing Academy in Los Angeles as he completes his preparations, also said the fight would never happen.
"The Williams sisters can play tennis against each other, the Schumacher's can race cars against each other, but boxing is completely different," he said.
"Money doesn't even come into it. What would be the cost to our mother (Nadezhda), it would kill her. We wouldn't want to break our mother's heart.
"We love our mother too much to do anything like that. We grew up together and our mum was always there taking care of us. And then to fight each other? No way! And she will never come to a fight."
Wladimir, who will be in his brother's corner when Los Angeles stages its first heavyweight title fight for 45 years, added: "There are four titles in world heavyweight boxing and we have big dreams to unite them. Two titles for him and two titles for me.
"Anyway, Vitali would win. He is stronger, taller, older, he has more power, more strategy and is more clever. Vitali has an unorthodox style but people underestimate him, just look at his record."
Klitschko has knocked out 31 of the 32 opponents he has beaten with his only defeat coming when he quit after nine rounds of a WBO title defence against Chris Byrd in April 2000 after tearing the rotator cuff in his left shoulder.
But along with brawn there is also a brain. Klitschko, nicknamed Dr Iron Fist, has a doctorate in sports science and philosophy, speaks four languages and, like Lewis, lists chess as a hobby.
"It's difficult to say if having a PhD has helped me because when you fight in the ring you don't have to be intelligent.
"But in preparing you have to analyse many things and then you have to use your head. I am ready mentally to fight Lewis, I've studied him for a long time.
"This is the chance at the title I have been waiting for and I am 100% ready for this fight. I have been preparing for this fight for over a year because I knew I would fight Lewis sooner or later.
"I have seen videos of Lennox in action many times. He is a great sportsman and I've seen the strong side but I've also seen his weaknesses."