The 34-year-old will call time on his City career at the end of the season following 10 trophy-laden years at the Etihad Stadium.
"I moved to Eibar a very short time before the beginning of the 2004-05 season and it was the only one available," he told the club's magazine.
"It was given to me. Then I moved to Celta on loan and 21 was already taken, so I took the number 16.
"Afterwards, I went back to Valencia and 19 and 21 were the only numbers left.
"And here's an anecdote I never told to Jaime Gavilán. That year when both of us arrived there, 19 and 21 were the only squad numbers available, and I got on really well with Curro Torres.
"Me and Gavilán, both newcomers, held a raffle and in a moment when he was distracted, Curro told me which one to pick. It was hidden in his hands and I picked the one with the 21.
"We cheated a little bit there… and Gavi was never aware of that.
"And I've been wearing the 21 shirt until now… and I never told him! I hope he will understand…"