'The King of the Stretford End' cut the ribbon at a ceremony inside Old Trafford on Thursday alongside chief executive David Gill and signed autographs for supporters.
"It's very nice of Manchester United to do something like this," he told ManUtd.com. "It really is. It's nice to be remembered. The way they've presented it is absolutely fantastic and there are some photographs I haven't seen before.
"The 50 years have absolutely flown by. When I was asked to do it, they said it was 50 years since you signed, and it really just rocked me. It's in the back of your mind and I guess you do know but it still seems incredible.
"When I signed, I could not have imagined this. I'm very grateful and honoured really that a club like Manchester United have such things in the ground. It is just lovely."
Gill also spoke fondly about the former Scotland international, undoubtedly one of the greatest players in the glorious history of the club.
"He was a fans' favourite from the beginning," he recalled. "He's still the second-highest scorer at United, behind his good friend Bobby [Charlton]. We've got some fantastic memorabilia, some of it previously unseen, and it's fantastic.
"It shows Denis' importance at the club that he's the only person to have two statues. The Trinity one with Sir Bobby and George Best and also the very big one in the Stretford End.
"Also, the museum itself has had a brilliant year. I'm very pleased because all the staff have