The Real Reason Behind Sir Alex Ferguson's Retirement?

On 8 May, the BBC shared the news:

There has been enormous interest in this decision … even in Canberra.
On 9 May the Canberra Times ran a story around “the greatest coach?” with an excellent interactive infographic.

I have looked at a lot of the coverage and have yet to find anyone who has pinpointed the real reason for Sir Alex’s retirement.
I think it has a great deal to do with my Aunty Doris. She was a passionate Manchester United supporter for over eighty years. Sadly she passed away on 1 April this year. She was a champion advocate for Alex Ferguson when he was appointed and she kept a close eye on him throughout his tenure.
Her memory of Manchester United performance was encyclopaedic. She was in her early 40s at the time of Munich air disaster. When I last saw her in 2011 we spent some time discussing Duncan Edwards and then talked about a survivor of the crash, Sir Bobby Charlton.
Six years ago, Aunty Doris went to a game at Old Trafford to celebrate her 90th birthday.
I may be mistaken but with an Aunty Doris size hole in the universe, it would have been very difficult for Sir Alex to carry on.
As we said goodbye the last time we met, I am sure I heard Aunty Doris say as I was leaving “Don’t get me started on Eusebio …” and I think she was starting to re-analyse the 1968 European Cup Final.
That is the kind of person you need in your Boot Room.

 Postscript

Aunty Doris’s grandson, Rhys, alerted me her appearance in Google Street view. Incredible.