Roger Federer is more than the tennis GOAT—he's one of the world's biggest tennis fans.

The world No. 1, like many fans around the world, is buzzing over episode 29 of the Venus vs. Serena rivalry at Indian Wells tonight.

Watch: Venus vs. Serena By the Numbers

The 20-time Grand Slam champion said the sisters' story has been fascinating for him to follow from the very start.

"They had a massive arrival on the scene, a lot of buzz around them, and they lived up to the hype. Came out and crushed it," Federer told the media after dismissing 25th-seeded Filip Krajinovic to reach the Indian Wells round of 16. "From the very beginning, they were very interesting to follow. I think they hardly played any juniors, really, which made it more of a mystery, because you just didn't know exactly what to expect from them. And coming, you know, from being coached by their dad. I mean, it's an incredible fascinating story, like you said.

"And then for many years we were worried that they were going to check out early with sickness or injuries. We weren't sure if they're going to play as long as we hoped them to play. And here we are. They are both over 35, 36, and still basically playing at the top. Serena being a mom now, Venus overcame a lot of also difficult situations and still playing." 

The father of two sets of twins—eight-year-old daughters Myla and Charlene and three-year-old sons Lenny and Leo—said Serena, who launched her comeback at Indian Wells after giving birth to her first child, daughter Alexis Olympia in September, can be the story of the year.

"Being older again than Serena, myself, it's wonderful to see and I'm very happy for them, you know, especially now watching Serena's comeback since the baby," Federer said. "I think that's going to be a huge story, maybe the story of the year. Hopefully she decides to play a lot and enjoy herself in the process and get back to who knows how high? It almost doesn't matter, but it would just be amazing to see her do it now.

"And then now they are facing off here tonight. I think it's great for the sport and they have done so much already. This is like, you know, the extra lap they are doing and the fans can enjoy it. So I'm very happy for them."

Photo credit: Wimbledon