The Duchess of Cambridge has been forced into self-isolation for 10 days after coming into contact with someone who later tested positive for coronavirus.
Kate, 39, had two engagements scheduled on Monday as she and Prince William were both meant to celebrate the 73rd anniversary of the NHS by attending the service of thanksgiving in St Paul's Cathedral ahead of an NHS Big Tea at Buckingham Palace.
Kensington Palace said in a statement: "Last week The Duchess of Cambridge came into contact with someone who has subsequently tested positive for COVID-19.
"Her Royal Highness is not experiencing any symptoms, but is following all relevant government guidelines and is self-isolating at home."
Prince William is still due at St Paul's Cathedral on Monday morning as part of a day of thanks for the NHS for the hard work of staff during the COVID-19 pandemic, but Kate will have to miss out.
Kate went on her own to Wimbledon on Friday, and was with William and their son George at Wembley Stadium earlier in the week.
She toured the kitchens, and watched Jamie Murray in doubles action with Tim Henman. She would usually attend the men's finals on the last day of the fortnight but will probably have to miss out now.
It's reported she was alerted about the possible exposure that afternoon and began self-isolating on Friday.
It means she would not be on hand to present the trophy to the winner in her capacity as patron of the All England Lawn Tennis Club.
It's not known which of her contacts has contracted COVID.
Both Kate and William have had their first vaccinations against COVID-19, sharing pictures of them receiving the jabs at the Science Museum, near to their home of Kensington Palace.
According to the Daily Mail's royal editor, Kate has had her second jab too.
Rebecca English said on Twitter that Kate "regularly undertakes lateral flow tests as part of the Royal Household testing regime and before engagements".
According to PA, both tests taken before she went to Wembley and Wimbledon were negative.
Prince William can still take on engagements with social distancing in place.
Among the guests at St Paul's on Monday morning are NHS England chief executive Sir Simon Stevens, matron May Parsons, who administered the first COVID-19 vaccination outside clinical trials, and Sam Foster, the nurse who gave the first Oxford AstraZeneca jab.
Staff who battled the virus themselves and staff who treated the first patients in England will also be there.
Kate was set to help William, 39, host a Big Tea event at Buckingham Palace after the service.
Ahead of the event, Alexandra Heys, nurse ward manager in the respiratory high care unit at Gloucestershire Hospitals NHS Foundation Trust, said: “The special tea at Buckingham Palace means a lot to NHS staff who have been through so much over the last year, and I feel so honoured to be meeting the Duke and Duchess of Cambridge today.
“I know from personal experience that the past year has taken a huge toll on NHS staff who have worked incredibly hard to take care of patients during a challenging time.
“My team at the respiratory high care unit has cared for over 300 very sick Covid patients, all of whom required dedicated around-the-clock care.
“All NHS staff have gone above and beyond, providing additional care in difficult circumstances, including connecting isolated and very sick patients with their families in their most challenging moments.
“We have all been through a lot, so seeing the public get behind the NHS Big Tea on such as massive scale is an immense boost and really makes a difference.”
The duke and duchess became joint patrons of NHS Charities Together in December 2020.
Watch: Duchess of Cambridge cuts the perfect strawberry at Wimbledon