The Serbian tennis player is the first man since 1948 to save championship points in the final and go on to win.
The 5-year-old royal also has another connection to Serena Williams.
The Swiss tennis champ is currently competing at Wimbledon.
The two tennis greats competed in the United States vs. Switzerland mixed doubles match at the Hopman cup.
The tennis legends will play a mixed doubles match on New Year's Day at the Hopman Cup in Australia.
The Serbian tennis star bested South African eighth seed Kevin Anderson.
The show of emotion triggered a standing ovation in the terraces.
"Would you describe your game as a silky gazelle?"
The duchess wasn't sparing with her smooches. 😘 😘 😘
Federer claimed victory in less than two hours.