Tennis legend, Serena Williams, who boasts an incredible 23 Grand Slam titles, has been turning heads on Instagram as she showed off her impressive post-retirement fitness journey with her 18.1 million followers.

Serena Williams is proving that retirement hasn't meant slowing down, especially when it comes to fitness. The tennis legend, with an impressive 23 Grand Slam titles under her belt, hung up her racket after a gripping final match at the U.

Serena Williams posted a series of gym selfies showing off her toned physique after telling fans in December that she had met her weight loss goal.