The Scottish tactician, who had Bruce as his captain at Old Trafford when he kicked off, marks 25 years in charge of United this weekend when Sunderland come to town and the Black Cats manager feels an achievement like this will never be matched.
"To do 25 years? It will never be done again, never, especially at a club like Manchester United, where the huge demands on you are quite incredible," Bruce said.
"But he seems to thrive on it. I spoke to him this morning at 7.40am, which is typical of him.
"A game last night and he is in the office at 7.40am this morning, which is quite remarkable."