Britain's Kate, The Duchess of Cambridge and Prince William watch Serbia's Novak Djokovic play Switzerland's Roger Federer during the men's singles final match of the Wimbledon Tennis Championships in London, Sunday, July 14, 2019. (AP Photo/Tim Ireland)

Switzerland's Roger Federer is dejected after losing a point to Serbia's Novak Djokovic during the men's singles final match of the Wimbledon Tennis Championships in London, Sunday, July 14, 2019. (Adrian Dennis/Pool Photo via AP)

Switzerland's Roger Federer returns the ball to Serbia's Novak Djokovic during the men's singles final match of the Wimbledon Tennis Championships in London, Sunday, July 14, 2019. (AP Photo/Tim Ireland)

Serbia's Novak Djokovic is dejected after losing a point to Switzerland's Roger Federer during the men's singles final match of the Wimbledon Tennis Championships in London, Sunday, July 14, 2019. (AP Photo/Tim Ireland)

Switzerland's Roger Federer plays a return to Serbia's Novak Djokovic during the men's singles final match of the Wimbledon Tennis Championships in London, Sunday, July 14, 2019. (Laurence Griffiths/Pool Photo via AP)