Roger Federer's decision to retire from tennis is a "sad day" for sport, his great rival Rafael Nadal has said.
Only Spain's Nadal, with 22 majors, and Serbia's Novak Djokovic, with 21, have more men's Grand Slam singles titles than the 41-year-old.
"Dear Roger, my friend and rival. I wish this day would have never come," Nadal posted on social media.
"It's a sad day for me personally and for sports around the world."
Nadal defeated Federer 24 times in 40 matches during one of the most celebrated rivalries in tennis history.
"It's been a pleasure but also an honour and privilege to share all these years with you, living so many amazing moments on and off the court," Nadal said.