Sir Alex Ferguson said he made the decision to retire from football last Christmas after his wife's sister died.
He told Sky Sports: "Things changed when Cathy's (Sir Alex's wife) sister died, she's isolated a lot now and I think I owe her a lot of my own time.
"For 47 years she's been the leader of the family, looked after our three sons and sacrificed for me, now she's got lots of grandchildren, they all dote on her and I think she's lost her best friend, so I think I owe her time.
"Also, it is important to go out a winner, that is really important at this club."
More top news
Pregnant women who smoke are more likely to give up if they are given shopping vouchers, new research suggests.
Children are eating the equivalent of seven and a half chocolate fingers for breakfast, campaigners have warned.
Stephen Fry has suggested that the "the patter of tiny feet" may be on the agenda following his wedding to Elliot Spencer.