Cristiano Ronaldo's move from Manchester United to Real Madrid in 2009 will forever be remembered as one of the biggest ever.
Not only for the price, either, which broke the world record at £80m.
It was a transfer that changed the game, really, beginning a new era for not just Real but world football.
Los Blancos had their superstar, the player who would guide them through a highly successful period in their history - and their answer to Barcelona.
The Catalonians had just swept up every trophy available in Pep Guardiola's debut season as boss, reinventing the way the game was played and inspiring a shift in tactics all over the world.
They looked set for long-term domination and Real's answer was to spend big under returning president Florentino Perez.
The likes of Kaka and Xabi Alonso also arrived but Ronaldo was the star and the player they hoped would stop Barcelona in their tracks.
But things could have turned out differently if United boss Sir Alex Ferguson had got his way - about as different as you can imagine, actually.
Ferguson didn't want Ronaldo to leave United but after realising he couldn't change the player's mind, he had a different plan - anywhere but Real.
The Scot was open with his dislike of Real, saying in 2008 that he wouldn't 'sell them a virus', let alone his best player.
Realistically, only one other club could have afforded Ronaldo in 2009 - Barcelona.
Ferguson apparently contacted them, per AS, and encouraged a bid, only for it to turn out that Ronaldo's mind was set on Real and he wasn't changing it.
It's amazing to think of how much things would have changed if Ferguson had his way.
Messi and Ronaldo would have played together, for one thing, cancelling out possibly the game's greatest ever rivalry.
It also seems impossible to overstate how dominant Barcelona would have been with both in their side - or how much weaker Real would become.
As it turned out, Ronaldo reportedly had a deal with Real that meant he couldn't change his mind.
You can't help but wonder 'what if?', though.