• Federer was first blessed with twin girls in 2009
  • Federer says that's when he began to question his future
  • The 20-time Grand Slam winner has no plans of retiring any time soon

Roger Federer has revealed that he began to question his future after his daughters were born in 2009.

Federer and his wife Mirka were blessed with two daughters in 2009 and interestingly, the couple had another set of twins, boys this time, in 2014. Both the set of twins are identical and the Swiss Master had earlier admitted how he used to have nightmares trying to tell his twins apart.

Speaking about his future in a recent interview, Federer said, "I know I am not eternal, like normal it is, and to be honest it's from when the daughters were born (in 2009) that I started questioning myself on my future. But then my body gives me good signs, the family supports me and they are happy to travel around the world with me. That's crucial. When the body will no longer hold up and my family will be tired, I will stop. But I do not think it will happen anytime soon. I still enjoy playing."

The veteran explained how his rivalry with Rafael Nadal has been a blend of good and disappointing memories on the court.

"Rafa broke through very early, our best moments often coincided, some of our matches became historical, unfortunately, I also went through some of my most disappointing losses against him in my career. And then he is a lefty, he forced me to find different ways to compete against him. Let's say that in the beginning, Novak was the man who I faced in the semifinals and Nadal the finals man, now the situation changed and that's also because of Djokovic."

Roger Federer advanced to the US Open quarter-finals by winning in only 79 minutes on Sunday

When Federer was asked to pick between winning a Grand Slam or the Olympic Games, the 38-year-old instantly denied answering that.

"That's impossible. Grand Slams are our daily things and my most emotional win was the 2009 French Open, even more than Wimbledon because I sought it for so long. But the Olympics is something that happens once every four years, it's something different, you represent your country, you know the athletes coming from around the world. I would not be able to choose, really. We will see what happens."