Lip reader Jeremy Freeman claimed to the Sun that Kate told Charlotte to “come over here” as they got to their seats, before thanking the lady who accompanied them and waving to the crowd.
The royal said “hi” to the spectators and watched as people kept being up on their feet applauding.
She then turned to the lady next to her and commented “so sweet”.
Later, Kate went from the stands down to the playing surface to present the trophies, part of her duties as patron of the All England Club, which hosts the annual tournament.
She shook hands with some of the ball kids who worked at the tournament, then exchanged words with both players and applauded Alcaraz after giving him the winner’s trophy for the second year in a row.
During a conversation in a room inside the tournament’s main stadium after the trophy ceremony, the royal told the tennis star: “You played so well. Enjoy the win.”
Kate was also joined by her sister, Pippa Middleton, who sat next to her and Charlotte during the match.