The Portugal international is expected to complete his dream move to the Santiago Bernabeu by the end of June and he will leave Old Trafford "with our blessing", according to Charlton, who also described the fee as "vulgar".
Ferguson fought long, hard and, sometimes, publicly, on his mission to defy Real's overtures so it curious that he has kept a diplomatic counsel on the loss of his most prized asset.
The sale of Ronaldo has been greeted with open arms by rival Liverpool, Chelsea and Arsenal supporters. Charlton, however, who has witnessed the departures of former favourites such as Bryan Robson, Eric Cantona, Roy Keane and David Beckham, has insisted it would be folly to write Ferguson off just yet.
The wily Scot has been given the Glazer family stamp of approval to strengthen his attacking options and Charlton would not be surprised if he had one last trick up his sleeve.
"He is a great judge of player. Alex Ferguson is very brave, he's very brave with his decisions, he's very decisive with his decisions, and that is why he's been a major success," Charlton said.
Ferguson has been linked with close-season swoops for Franck Ribéry of Bayern Munich and Antonio Valencia of Wigan.
Nick Walsh writes about football betting for Betfair