Serena Williams welcomes Federer to retirement: 'I have always looked up to you'

Serena Williams welcomed Roger Federer to the tennis "retirement club" on Thursday, saying she has always admired and looked up to the Swiss legend.

On Thursday, Federer, a 20-time Grand Slam champion, announced his retirement after playing next week in London at the Laver Cup.

Among those sending congratulations to the 41-year-old icon for his tremendous career was 23-time Grand Slam winner Williams, who said she was "evolving" away from tennis, with last week's US Open expected to be her final tournament.

"I wanted to find the perfect way to say this, as you so eloquently put this game to rest -- perfectly done, just like your career," Williams said in an Instagram post.

"I have always looked up to you and admired you. Our paths were always so similar, so much the same. You inspired countless millions and millions of people -- including me -- and we will never forget."