Kate reportedly found out the bad news around 4 p.m. after she sat down in the Royal Box, and she is believed to have left the stadium before athlete Dan Evans began his match.
The mom-of-three is self-isolating for 10 days, as she came in contact with someone who tested positive for COVID-19.
"Last week, The Duchess of Cambridge came into contact with someone who has subsequently tested positive for COVID-19," her spokesman said. "Her Royal Highness is not experiencing any symptoms, but is following all relevant government guidelines and is self-isolating at home."
Fortunately, the brunette beauty began the vaccine process in May.
"Yesterday I received my first dose of the COVID-19 vaccine at London’s Science Museum. I’m hugely grateful to everyone who is playing a part in the rollout - thank you for everything you are doing," she wrote via Instagram at the time.
For his part, Prince William wrote about his experience around the same time.
"On Tuesday I received my first dose of the COVID-19 vaccine. To all those working on the vaccine rollout - thank you for everything you've done and continue to do," he captioned a photo of himself getting pricked on the official The Duke and Duchess of Cambridge social media accounts.
William contracted the virus last year and was reportedly "hit pretty hard" and "struggled to breathe."
Even though Kate wore a mask when she arrived to the sporting event, journalist Julia Hartley-Brewer was annoyed she took off her face covering while in the box.
"God but this makes me angry," she wrote on Twitter. "All the rich people are happily enjoying Wimbledon without wearing masks while the staff and the ball girls & boys are forced to cover their faces."