Individually, they're two of tennis' greatest stars, and they have also endured a rivalry worthy of legendary status - contesting perhaps the greatest match in the sport's history, the 2008 Wimbledon final.
Roger Federer and Rafael Nadal share 37 Grand Slams, and are known for facing off against each other, rather than teaming up.
The one rare example was at last year's Laver Cup, where the two partnered up to play doubles in a fearsome combination.
And although somewhat unexpectedly, it has been revealed that Nadal approached Federer, around a decade ago, as the two approached the peak of their respective careers, to play together on the ATP tour.
The Spaniard's enthusiasm was not shared, however, as Federer revealed he rejected the proposal - mainly due to the fact the pair were fighting each other for slams at the time.
"Rafa asked me to play doubles in I think it was Madrid indoors or so, but then I think our rivalry was so intense, I just felt like it was the wrong thing to do," Federer revealed.
"As you say, could be like a conflict and not something we should be doing. It would have been great for the game, but I think it would have been a bit of a curveball for everybody. It was a fierce rivalry, now all a sudden they're being friendly."
The eight-time Wimbledon champion also questioned how satisfied people would have been to see himself and Nadal suddenly on the same team.
"I don't think the press would have enjoyed that so much.
"They want to put us against each other, not with each other, but today I think we're much more laid back, me especially, too, because I didn't have a rival for a long period of time, and then Rafa came up and there was -- it was great, but I just didn't feel like we needed to play doubles together."
Federer's decision to decline almost certainly helped to keep the edge between the players at key points in their careers.
Still, no-one can deny that a Nadal-Federer team would be one of the most enjoyable to watch, and also a force to be reckoned with.