Tennis fans were left devastated after Roger Federer and Serena Williams retired from the sport within days of each other.

Federer played his last tennis match at the 2022 Laver Cup in London, with the 20-time Grand Slam winner citing a knee problem as the reason behind his retirement.

He posted a statement on social media, telling his fans he "must recognise when it is time to end my competitive career".

The Swiss star is not the only tennis legend to retire in September 2022, with 23-time Grand Slam winner Serena Williams also “evolving away from tennis” following her third round exit at the US Open.

Federer and Williams have been clear about their admiration for each other during their respective careers, and were particularly effusive during a joint interview at the Hopman Cup in 2019.

Touching interview with Serena Williams and Roger Federer

The pair had just come up against each other in a competitive match for the first time ever, with Federer and Belinda Bencic emerging triumphant from the mixed doubles rubber.

When asked about the occasion, Williams found it impossible to contain her excitement.

“It was super cool that we got to do it, at such a pinnacle point in both our careers,” she enthused.

“For me, it was super cool. Literally wanting to take pictures. I wanted to bring my baby out. Like way too excited. But it was really fun.”

Federer then raved about Williams, complimenting her serve in particular.

“Well, I was nervous returning, because you just don't know. People talk about her serve so much, and I see why it is such a wonderful serve, because you just can't read it.

“It was a bit nerve wracking to be honest, because all of a sudden you're serving, especially the last serve, I'm like, ‘I’ve got to win this point but it's Serena Williams!’

“I was telling myself, maybe this is what I've always wanted, the big moments like this. I made the serve but actually totally missed the target, and thank you for missing the ball.

“But it was great fun and yeah, she’s a great champion. You see how focused and determined she is and I love that about her.”

Video: Watch brilliant interview with Serena Williams and Roger Federer

Williams then returned the favour, showering Federer with compliments.

“Well, I mean, the guy is great. I mean, he's the greatest of all time, to be honest. On the court and off the court, he has such charisma. He's just a wonderful player.

“I think his serve is super underestimated, he has a killer serve. Literally, you can't read it and there's a reason why he's the greatest. You can't be that great and not have such an awesome weapon like that serve.

I watched him all the time, but I never knew how amazing it was. So it was really cool to kind of learn, hopefully I can get some tips later on how to get a little better, but it was really impressive.”

What have Roger Federer and Serena Williams been up to since retirement?

Federer has taken some time to relax after stepping back from tennis, returning to Switzerland for a period, before embarking on trips to Japan and the United States.

He was honoured at Wimbledon earlier this month, sitting in the Royal Box on Centre Court to watch the day's tennis unfold. Prior to this, he joined Coldplay for a song during their concert in Zurich.

Williams said she would be focusing on her venture capital firm 'Serena Ventures' after retirement, and she also announced her second pregnancy in May.