Sir Alex Ferguson says he made his mind up to retire in December.
There have been plenty of questions asked about when the Scot made up his mind to go, with some wondering whether he had been eased out given last week's programme notes in which he insisted he was staying, or whether it had something to do with his health.
However, after the 2-1 win over Swansea, Ferguson insisted neither theory was true.
"I decided at Christmas," he said.
"Cathy's sister died. She had lost her best friend and she has been isolated.
"For 47 years she has been the leader of the family. She has made a lot of sacrifices for me."
It was a touching reference to his wife, who has been responsible for bringing up their three children as Ferguson powered along as the most successful British manager of all time.
And he admitted the news nearly slipped out on a couple of occasions before Wednesday's public announcement, which came a day after the intense rumours about his future first surfaced.
"It was difficult to keep it a secret," he said.
"Sometimes we nearly blurted it out to the family and we told our sons in March but my brother didn't know until Tuesday.
"I wanted to tell the players first and also my staff. Unfortunately there were rumours going around on Tuesday so we started to speed it up a bit."
Now the challenge of standing in Ferguson's mighty footsteps falls to David Moyes, whom the Scot urged supporters to stand by during his on-pitch post-game address prior to the trophy being handed over.
"I would like to remind you this club stood by me in bad times, the players and the staff," he said.
"Your job now is to stand by the new manager."
Ferguson also paid personal tribute to Paul Scholes, who started yesterday's game and will also retire in the summer, and Darren Fletcher, who continues his recovery from a chronic bowel condition.
And he insisted he would still be a regular presence at Old Trafford.
"I will be able to go along and watch them rather than suffer with them," he said.
"Those last-minute goals, the comebacks and even the defeats are part of this great football club. It has been an unbelievable experience.
"I have been fortunate to manage some of the greatest players in this country, let alone Manchester United.
"They have represented our club in the proper way."
Ferguson said he had "no speech in mind" and would just "ramble on" before admitting at one point that he might start "bubbling".
"I wish the players every success," he said.
"I know how good you are. You know the jersey you are wearing and you know what it means to everyone here. Do not let yourselves down."
Javier Hernandez put United ahead yesterday and though Michu equalised just after half-time, Rio Ferdinand's 87th-minute winner ensured a fitting climax to Ferguson's Old Trafford experience, which has left new arrival Robin van Persie spellbound even though he has only been at the club for a year.
"It was a really sad day when Sir Alex told us what was happening," said Van Persie.
"But everyone understands it and from my point of view it has been a great honour," he added.
"One year is not a lot but he is a great manager and a great person. The way he handles players is unbelievable."
Ferguson was not the only person to bid farewell to Old Trafford.
As is his style, Scholes disappeared into the shadows quietly, having returned to the fray for his farewell appearance after a three-and-a-half month absence.
But in the same way as Ferguson made his mark on Van Persie, so did 38-year-old Scholes.
"Scholesy is unbelievable," said Van Persie.
"When I first came to England I saw things I never saw before from players like Bergkamp, Henry and Pires.
"Since I came here, I have that feeling again. Scholesy can do things I have never seen in my life."
Ferdinand's winner – his first goal in five years – ensured Ferguson left Old Trafford a winner.
Hernandez's goal was his 17th of the season and arrived in the 39th minute, Michu's equaliser coming four minutes after the break. Then came that late, and fitting, winner.