Manchester United boss Sir Alex Ferguson admits he decided to retire before Christmas.

His final game at Old Trafford was Sunday's 2-1 win over Swansea, which was followed by his 13th Premier League trophy presentation.

"I decided at Christmas," he told Sky Sports.

"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."

He added: "It was difficult to keep it a secret.

"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."