It's her party, and she will wear a He-Man costume if she wants to. On Sunday, Serena Williams posted a picture of herself rocking a blonde wig, metal breast plate and some serious muscle definition (the latter was not exclusive to the costume).

The 21-time Grand Slam singles champ posed alongside actor and model Colton Haynes, who donned an equally impressive Maleficent costume:

A photo posted by Serena Williams (@serenawilliams) on Apr 17, 2016 at 3:44pm PDT

While any superhero costume would be befitting of the reigning Wimbeldon and French Open winner -- who has displayed supernatural talent on the tennis court time and time again -- this was a cheeky selection on her part.

Williams has long been the subject of criticism for her muscular physique and has openly dealt with overcoming body-image issues. Earlier this year, in an interview with Time magazine, the tennis phenom explained: "It has been a struggle to love my body, but now curves are in and I'm happier in myself."

Slay, Serena. Haters, you've been put on notice.

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