It will be the costliest transfer deal in football history — yet it took only a couple of hours to complete.

When the world’s biggest club, Real Madrid, faxed the world’s second biggest, Manchester United, with an £80m offer for Cristiano Ronaldo on Wednesday evening, there was only going to be one outcome.

United have tried for over a year to fend off the Spanish giants but even they have their price — and now Real Madrid are going to pay it.

Ronaldo himself will, of course, be quids in after the world record deal goes through; his new salary is believed to be a basic £9m a year over the course of a six-year contract.

That already considerable figure may well rise by 25% each year — to offset a non-domicile tax of that percentage of his income — meaning that by the end of his current contract at the Bernabeu, Ronaldo could well have pocketed a staggering £106m.

United fans meanwhile have mixed feelings about the Portuguese superstar’s departure.

In his six years at Old Trafford, the sublimely gifted Ronaldo helped re-establish United as Premiership champions and it was his goal against Chelsea last year that put them on their way to winning the Champions League.

But his displays of on-the-field petulance, along with the growing suspicion that his heart lay with boyhood heroes Real Madrid, soured the love affair somewhat.

And when Real Madrid president Florentino Perez faxed United’s chief executive, David Gill, at Old Trafford with the unprecedented offer on Wednesday evening, the Red Devils made little effort to discourage the potential buyers.

When made aware of the offer, United manager Sir Alex Ferguson, who was holidaying in the south of France, recommended that it be accepted and so did the Glazer family, who own the club and are having to service a £650m debt.

“Manchester United have received a world-record, unconditional offer of £80m for Cristiano Ronaldo from Real Madrid,” said the club in a short statement yesterday.

“At the request of Cristiano — who has again expressed his desire to leave —and after discussion with the player’s representatives, United have agreed to give Real Madrid permission to talk to him.”

United expect the whole process to be concluded by the end of this month, which is bound to raise suspicion that a deal had already been done — given that the June 30 date just happens to be exactly the same as the one that was supposed to trigger a £20m compensation package for Ronaldo from Real if no transfer had been completed.

“There is no information that this is is anything other than the manager’s decision, but obviously there is huge pressure on the owners and it is a temptation when you are offered that much money,” said Duncan Drasdo, chairman of the Manchester United Supporters Trust.

“That is exactly why we want to see a commitment from the owners that the money is going to remain within the club and available to strengthen the squad.

“We have sold the best player in the world. That is a big disappointment. If the money is reinvested into the club at least it will soften the blow.”

Old Trafford insiders have attempted to assure supporters that is the case and also insist no agreement was in place when Ferguson famously declared last year that “he would not sell that mob a virus”.