Serena Williams' Grand Slam titles

Serena Williams poses with the Wimbledon trophy after defeating Angelique Kerber 7-5, 6-3 for her 22nd major title.

Serena Williams poses at the trophy presentation after winning her match against Garbiñe Muguruza to claim the 2015 Wimbledon women's singles title.

Serena Williams takes a selfie with the Suzanne Lenglen trophy following her victory over Czech Republic's Lucie Safarova after the 2015 French Open women's singles final match.

Serena Williams jubilates after winning the 2015 Australian Open women's singles final against Maria Sharapova of Russia.

Serena Williams hugs the 2014 U.S. Open trophy after beating Caroline Wozniacki in the women's singles final.

Serena Williams celebrates after defeating Victoria Azarenka in the 2013 U.S Open women's singles final.

Serena Williams celebrates after recording match point against Maria Sharapova in the women's singles final of the 2013 French Open.

Serena Williams poses with the 2012 U.S. Open championship trophy in Central Park the day after defeating Victoria Azarenka in the women's singles final.

Serena Williams, left, and Agnieszka Radwanska hold up their trophies after their match in the women's singles finals of the 2012 Wimbledon Championships. Williams won 6-1, 5-7, 6-2.

Defending champion Serena Williams reacts as she defeats Vera Zonareva to win the 2010 Wimbledon women's singles final.

Serena Williams collapses on the court in celebration after winning the 2010 Australian Open women's singles title.

Serena Williams holds the 2009 Wimbledon trophy after defeating her sister Venus on Centre Court.

Serena Wiliams celebrates after defeating Dinara Safina of Russia in the 2009 Australian Open women's singles final match.

Serena Williams celebrates with the 2008 U.S. Open trophy after her win over Jelena Jankovic of Serbia.

Serena Williams plays a backhand against Maria Sharapova during her women's final match of the 2007 Australian Open. Serena won the match for her eighth Grand Slam.

Serena Williams, left, and compatriot Lindsay Davenport, top seed, hug each other after their women's singles final match at the 2005 Australian Open. Williams won the match, 2-6, 6-3, 6-0.

Serena Williams (left) holds the 2003 Wimbledon trophy after beating her sister Venus in the women's singles final.

Serena Williams poses for pictures with the 2003 Australian Open women's singles trophy on the banks of the Yarra River following her win. Serena beat her sister Venus 7-6, 3-6, 6-4 in the final.

Serena Williams, left, celebrates winning the 2002 U.S. Open against her sister Venus.

Serena Williams, left, holds her trophy after defeating her sister Venus, to win the Wimbledon women's singles final.

Serena Williams holds the Roland Garros French Open trophy after defeating her sister, Venus Williams in the women's final.