The duchess gave a sartorial nod to the unofficial "Wimbledon whites" dress code - players must wear white attire, though attendees aren't obligated to - by wearing a short-sleeved white shirtdress for her visit on Tuesday.
Kate, Duchess of Cambridge gestures after taking her seat in the Royal Box on Centre Court on day two of the Wimbledon Tennis Championships.
She surprised fans by showing up at the tennis tournament, and has been praised for choosing a "normal" seat.
There, the Duchess-who is patron of the All England Lawn Tennis and Crocquet Club- sat next to Wimbledon Chairman Philip Brook.
The duchess watched the match with British tennis player Katie Boulter and retired British player Anne Keothavong - who is a former world number one.
In the royal box, she sat down to watch Federer take on South African Lloyd Harris, a match the Swiss won in four sets.
Venus knocked out of Wimbledon by a 15-year-old
She did just that, converting her fourth when Venus put a forehand into the net. I can't help but look inside of myself and be proud and be happy for her.
The Duchess of Cambridge opened up about her shyness during a heartwarming moment with schoolgirl at a picnic to celebrate the move of her Chelsea Flower Show garden. Kate accentuated her slimmer than slim waist with a black, Alexander McQueen belt tied in a bow, and a little basket purse, also from McQueen.
Kate, 37, is also said to be watching Serena Williams - who is good friends with Kate's sister-in-law Meghan Markle - on Centre Court later today as the American player tries to win her 24th Grand Slam title.
The pair were spotted laughing and cheering from the sidelines.
What do you think of Kate's dress?
Britain's Kate, the Duchess of Cambridge, visits her "Back to Nature" show garden during the press day for Hampton Court Palace Garden Festival in East Molesey, London, July 1, 2019.
Markle paired her dress with fashionable pointy flats from Aquazzura that retail for $737.