In a saga which unfolded within days, the five-time Ballon d'Or winner was originally linked with rivals Manchester City after making it clear that he wanted to leave Juventus.
However, United quickly emerged as the front-runners and suddenly, the Portugal star was back at the club he left 12 years ago.
Reflecting on the deal, England legend Lineker revealed United's executive vice chairman Ed Woodward popped over while getting one of the biggest deals in recent history done.
Speaking to BBC Sport, Lineker said: "I'll put my cards on the table.
"Ed Woodward's a good friend of mine and he's my neighbour. He signed Ronaldo when he was in my garden!
"It was awesome. I knew when he walked in and he was on the phone to [Ronaldo's agent Jorge] Mendes or someone. I hope I'm not giving too much away here, but he did sign him, so…yeah!
"I've got a fantastic picture of him on the phone with him in the back garden, which I might share one day with his permission."
The Portuguese forward didn't waste any time kick-starting his second spell at the club, netting three goals in three league starts and scoring in both of United's opening Champions League group games.
Ole Gunnar Solksjaer's side have had a mixed start to the campaign, only winning once in their last four games in all competitions.
United were knocked out of the Carabao Cup to former manager David Moyes' West Ham.
They are currently fourth in the Premier League, after failing to win their recent home league games to Aston Villa and Everton at Old Trafford.
The Red Devils' recent 1-1 draw to Everton saw Ronaldo dropped to the bench, with fans criticising Solksjaer's team selection.
The Norwegian needs to get back to winning ways quickly, with a tough run of fixtures against Leicester, Liverpool and Tottenham in their next three league games.