Federer has had a poor year by his own incredibly high standards, But it doesn't matter if he comes back or if he continues to decline—he will always be a legend of the game.
He is undoubtedly one of the greatest players ever, some even say he is the greatest.
And the man who overtook him looks set to become a future great. At just 22, I can't think of another player who has had so much success so early on.
Nadal really has had a wonderful year.
He has won eight singles titles, including a fourth successive French Open and a victory in perhaps the greatest tennis match ever played, to break Roger Federer's grip on the Wimbledon trophy.
He also went on a career-best 32 match winning streak, and has now secured the World No.1 spot—something we have known for a while would happen. He became an Olympic gold medallist over the weekend, just to cap the perfect year.
For a long time Nadal has been considered the King of Clay. He is the best around on the surface. Some say he, despite only being 22, is the best clay court player to have ever played.
Today, however, his transition from King of Clay to King of Tennis was confirmed. Whether he can maintain that status for as long as his predecessor remains to be seen, but Nadal certainly won't let go of that title without an almighty fight.
It also remains to be seen if Federer can bounce back from this disappointing year, and climb to the top of the mountain again. If he can, then it will show he has fantastic mental strength—and may just catapult him towards "greatest ever" status.
It's worth saying that Federer also won an Olympic gold, but in the doubles. He was again disappointing in the singles, losing to James Blake in straight sets.
I do hope Federer does bounce back, because I don't want his rivalry with Nadal to die down. It has the potential to be the best tennis rivalry ever, the 2008 Wimbledon final proved that.
I don't think anyone wants to see the possibility of another match like that go out of the window.
But, for now at least, Federer will have to come to terms with fact that for the first time in over four years, he can't call himself the No.1 in the world. Will we see the demise of one of the greats or the comeback of a champion?
Whatever happens, Nadal will be waiting, ready for his next challenge. He is the man to beat now. He is the world's No.1.
He is the King of Tennis.