'Your old friend is always cheering for you': Roger Federer pens letter to retiring Rafael Nadal

Roger Federer has a "few things to say" about his longtime rival, Rafael Nadal, as the Spaniard prepares for the final tournament of his tennis career. The 20-time Grand Slam singles champion penned an emotional letter to his longtime rival on social media on Tuesday, hours before Nadal was set to take the court for Spain's quarterfinal match against the Netherlands in the Davis Cup Finals for, possibly, the last match of his two-plus decades on tour.

In a verbose tribute that spanned three pages on Instagram, Federer saluted Nadal's "epic" career, one that the Swiss had a front row seat for.

He wrote that Nadal "challenged [him] in ways no one else could."

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"You made me reimagine my game—even going so far as to change the size of my racquet head, hoping for any edge," Federer, who lost 24 of his 40 career matches against Nadal, added.

"And you know what Rafa, you made me enjoy the game even more."

In his heartfelt words, Federer revisited the start and end of his and Nadal's careers as rivals. He recalled the first time the two even played, in Miami in 2004, where a 17-year-old Nadal announced himself by beating then-world No. 1 Federer in the third round, as well as the last time they shared the court together for Federer's own farewell match.

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"All that buzz I'd been hearing about you about this amazing young player from Mallorca, a generational talent, probably going to win a major someday—it wasn't just hype," recalled Federer of that day in Key Biscayne.

Eighteen years later, at Laver Cup in London, Federer said goodbye to tennis, and Nadal stood by his side as his Team Europe teammate and doubles partner.

"Sharing the court with you that night, and sharing those tears, will forever be one of the most special moments of my career," Federer wrote.

The touching tribute from Federer came a day after Nadal told reporters in Malaga that he hadn't spoken with the Swiss ahead of arriving in Malage, and that is his own goodbye is a "different situation" to Federer's as a member of the Spanish team.

"[O]f course that's going to be my last week on the professional tour, but I don't think going to be my last good-bye," he said, "so [there's] gonna be another chances to do something."

It's something that Federer is looking forward to, he said.

"Rafa, I know you're focused on the last stretch of your epic career," he wrote. "We will talk when it's done. For now, I just want to congratulate your family and team, who all played a massive role in your success.

"And 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."