The boss celebrates the remarkable landmark on Sunday after being appointed in 1986 and is vowing to continue in the job for as long as his health allows him.
"It's been a really fantastic spell for me and something you don't think is going to happen," he stated. "It's been a bit of a fairytale to last so long and I appreciate that.
"I've been very fortunate to have some of the best players in the game and, when I look back on these players I think about how fortunate I am. It's incredible when you look at who's been here - Bryan Robson, Norman Whiteside, Brian McClair, Mark Hughes, Paul Ince, Roy Keane, Eric Cantona. What a collection of fantastic players.
"It's hard to think I actually controlled all these players for so long. Today, we have so many players with different personalities from different cultures."
Even though the manager has overseen many changes to the game, he is still very much up for the challenge of keeping United competitive on all fronts.
"I'll continue as long as I feel healthy enough to do it," he insisted. "In management, things change as the years go on. It's different now even to seven or eight years ago. A lot of things have changed."