Cristiano Ronaldo told Patrice Evra he would return to Manchester United.
Ronaldo left Old Trafford for the Bernabeu for a world-record £80million fee in 2009.
However, the Portugal international endured a difficult time under Jose Mourinho and was planning to leave Los Blancos in 2013.
United won the Premier League title that year and Ferguson planned to bolster his ranks with Tottenham star Gareth Bale and Ronaldo.
But the Scot instead decided to call time on his 27-year spell in charge of the Red Devils.
“You know, you talk about the hardest moments [in my United career], I would say maybe this [Fergie’s retirement] is the one,” Evra said on the latest UTD Podcast episode.
“Two weeks before that, I remember there was a lot of media saying Ferguson will maybe retire next year, and he said, ‘Patrice, I will never retire. I will be here another 10 years.
“He then said: ‘My target is I’m 99 per cent sure we will have Cristiano Ronaldo and Gareth Bale. I just need these two players to win the Champions League again. Ninety-nine per cent’.
“And to be fair, when I speak with Cristiano, I ask him and he said yes to the boss, and was coming to join United. He told me this.”
Evra went one to explain how the squad was told of Ferguson’s retirement as two players got extended apologies.
“After two weeks, we were in the dressing room waiting,” he added.
“When we arrived at Carrington, I see all those cameras and I was like: Wow, someone has done something wrong. Maybe a player is the story again! Someone has done something wrong, we are in trouble’.
“But we arrived and people said, ‘Guys, you have to stay in the dressing room because the boss wants to have a chat’. And when the boss came into the dressing room to talk to everyone, it’s never good news.
“He came, and he said, ‘I’m really sorry. Some people have said that I’m going to retire even before I say it myself. That’s why you saw all those cameras. But I will retire because my wife needs me’.
“He apologised to [Robin] van Persie, he apologised to Shinji [Kagawa], because he just brought them. He apologised to them especially.”
Ronaldo won his fist of five Ballon d’Or trophies while at United in 2008.
He has earned a further four since and trails rival Lionel Messi by one.