Walking through the grounds, the royal couple looked happy to be back at the tennis tournament for the first time this year.
WATCH: Kate Middleton's best Wimbledon fashion moments
Kate, 40, waved as they crossed the bridge from the millennium building into Centre Court after arriving at the SW19 grounds via the players' entrance.
The royal couple, who were joined by the Chairman of the All England Club Ian Hewitt, took their seats in the Royal Box ahead of the men's singles quarter-final tennis match between Novak Djokovic and Jannik Sinner.
Kate seen waving at the crowds at Wimbledon on Tuesday
Before sitting down, they exchanged a few words with Britain's Got Talent judge David Walliams. It is not known how long Prince William and Kate will remain to see the game; they may even watch British hopeful Cameron Norrie take on Belgium player David Goffin, who are playing on No.1 Court.
Great Britain's Alicia Barnett and Jonny O'Mara will also be returning to the grass courts on Tuesday in the mixed doubles.
The royal looked lovely in a blue polka dot dress
At one point, Kate smiled to William after a tense rally won by the Italian player, which sparked tense "oohs" and "aahs" from the crowd before a huge wave of applause.
Kate smiles at her husband William
The Duke and Duchess were joined by Kate's parents Michael and Carole Middleton, who was wearing a white floral dress. Over the past week, Kate's parents as well as her brother James Middleton and his wife Alizée Thevenet have made appearances.
The couple seen in the Royal Box at Centre Court
Looking fabulous as usual, the mum-of-three wore a blue polka dot dress while Prince William, 40, looked handsome in a pale grey checked jacket and navy trousers.
The Duke and Duchess looked happy to be back on Centre Court
Kate's chic number, by Alessandra Rich, featured pleats going down its front, quarter-length sleeves, padded shoulders and a waist-accentuating belt. She paired the look perfectly with coordinating pointy heels and her signature wavy long hair.
David Walliams was also in the Royal Box
It's no surprise to see Kate at the Championships since she is patron of the All England Lawn Tennis Club, having taken over the role from the Queen back in 2016. She has been a regular at the tournament since before she became a royal.
There was a tense moment during the match
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