The five-time Ballon d'Or winner has agreed terms with United per a club statement and just needs to pass his medical.
Ronaldo was linked with a move to bitter rivals Manchester City and it sent social media into overdrive, in addition to his former teammates.
Ferdinand spoke at length about the discussion he had with 'CR7' and revealed what he told him.
"It's a beautiful day man... and when it's a beautiful day you've gotta wear shades," he said just hours before the transfer was confirmed.
"Sir Alex Ferguson would've been the exact same. He would've hated to see Cristiano in a Man City shirt, just like any other person that's been connected for a long period of time at this football club.
"I rang him straight away, what's going on? Tell me you're lying.
"Every type of no, no, no, in the conversation. I'm like all the fans, I'm exactly the same and we're all exactly the same about that. Please tell me you're not going."
He then went on to discuss Ronaldo's return to United and described it as 'the best' transfer possible.
"It's the best, we've seen some great signings this summer. Hopefully we are sitting here waiting for something to unravel at this point.
"Before the transfer window closes, hopefully Man United get what they're looking for."
Ronaldo could be in line to make his second United debut against Newcastle United on September 11.
He'll be United's fourth signing of the summer after the arrivals of Tom Heaton, Jadon Sancho and Raphael Varane.
The club finished second in the Premier League last season and 12 points behind bitter rivals City.
Ronaldo is said to be ready to return and conclude business he describes as 'unfinished.'
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