Sir Alex took charge of United when van Nistelrooy was just 10 years old. Since then, Ruud has forged one of the most successful professional careers of the modern era and now, aged 36, is enjoying retirement.
And still Sir Alex goes on.
"It is incredible," he said. "It is difficult to get your head around. Twenty-six seasons!
"Ten years in football is an awful long time for a manager to be at a club. He is going on and on. In three or four years we will be talking about 30 years. It is out of this world.
"But he's doing it. As he said, he has outlived death. He is outliving everyone."
Ruud was speaking to ManUtd.com, Manchester Evening News and PA Sport.