When we face big Life Moments, it’s often the people close to us who put things in perspective. So with tennis great Rafael Nadal about to retire after one final Davis Cup tournament, who better than Roger Federer to put an incredible career — and a rare friendship — in perspective.

“You made me reimagine my game,” Federer, one of the greatest tennis players in history, told Nadal, another of the greatest tennis players in history, in a message shared on Instagram and other platforms.

“Let’s start with the obvious: you beat me—a lot,” Federer said. “More than I managed to beat you. You challenged me in ways no one else could.”

Nadal is ending his tennis career with the Davis Cup, where he and Spain face the Netherlands in a “Final 8” showdown. He’s scheduled to play on Tuesday at 11 a.m. ET, in a match carried by the Tennis Channel. The tournament is being held in Málaga, Spain, from Nov. 19 to 24: the semifinals are set for Friday and Saturday, with the final played on Sunday.

Nadal, known for his never-say-die pursuit of every point in a match, has contended with a series of injuries in his career, from his feet and knees to hip surgery in 2023.

Because this is the knockout phase of the tournament, it’s uncertain which match could be Nadal’s last. But it’s certain that for Nadal, the 38-year-old who has won 22 Grand Slams, the week will bring a flood of tributes. None are likely to be more personal than the note from Federer, his on-court Swiss nemesis and off-court friend.

“As you get ready to graduate from tennis, I’ve got a few things to share before I maybe get emotional,” Federer said.

Federer mentioned how he changed to a new racquet head, seeking a way to combat Rafa’s power and skill. He mentioned their exhausting and thrilling battles on the court, playing together for tens of thousands of fans. He also mentioned … Nadal’s underwear.

“I’m not a very superstitious person, but you took it to the next level. Your whole process. All those rituals,” Federer said of the notoriously particular and precise Nadal. “Assembling your water bottles like toy soldiers in formation, fixing your hair, adjusting your underwear… All of it with the highest intensity. Secretly, I kind of loved the whole thing. Because it was so unique—it was so you.”

Federer cast back to Nadal’s brash arrival in 2004 wearing a sleeveless red shirt, his famous biceps powering him to a win over Federer, who was then a newly anointed No. 1. He spoke of how their rivalry became a shared path, one that ended with the two aging legends playing doubles together — and openly weeping together — in Federer’s last big match, at the Laver Cup in 2022.

“Twenty years later, Rafa, I have to say: What an incredible run you’ve had,” Federer wrote. “Including 14 French Opens—historic! You made Spain proud… you made the whole tennis world proud.”

“I want you to know that your old friend is always cheering for you, and will be cheering just as loud for everything you do next,” Federer said, signing his note, “Best always, your fan, Roger.”