The Sporting Lisbon whizz-kid concluded talks with The Red Devils to seal his five-year contract with the Premiership champions, and was pictured leaving Old Trafford on Tuesday.
United claimed the fee will be paid over two years, and the 18-year-old becomes the Manchester club's latest summer recruit. The sum includes the total outlay, incorporating associated costs involved in the deal such as the player's personal terms. It is understood that the actual fee is around £7.77 million.
"We have been negotiating for Cristiano for quite some time, but the interest in him from other clubs accelerated in the last few weeks, so we had to move quickly to get him," stated Ferguson.
"It was only through our association with Sporting that they honoured our agreement of months ago.
"He is an extremely talented footballer, a two-footed attacker who can play anywhere up front - right, left or through the middle.
"After we played Sporting last week, the lads in the dressing room talked about him constantly, and on the plane back from the game they urged me to sign him. That's how highly they rated him," he told United's official website.
"He is one of the most exciting young players I've ever seen."
Portuguese sources, which first revealed that the deal was done on Monday night, claim United had to up their bid in order to fend off interest from Chelsea, who offered the more attractive option of loaning Ronaldo back to Sporting for another season.
This is a deal the Lisbon club preferred to arrange with United, but Ferguson wants the teenager to give him more options instantly in attack, after the failure to land Ronaldinho.
Ronaldo's potential is enormous, but whether he can shoulder the burden of providing the missing flair in attack for United, alongside Ruud van Nistelrooy, from the outset will be a source of much debate.
