Prince William was unwell with COVID-19 earlier this year but it was not publicly announced because he “didn’t want to worry anyone”.
Prince William has not publicly confirmed that he had the virus, but according to reports he told one observer at an engagement: “There were important things going on and I didn’t want to worry anyone.”
When contacted on Sunday, Kensington Palace declined to comment but did not deny the claim.
A source earlier told The Sun that the prince had been “hit pretty hard by the virus”, adding that it “really knocked him for six”.
The duke was treated by palace doctors and followed government guidelines by isolating at the family home Anmer Hall, in Norfolk.
Despite his illness, he still managed to carry out 14 telephone and video call engagements in April, including phoning NHS workers at Queen’s Hospital in Burton.
William, who is father to George, 7, Charlotte, 5, and Louis, 2, had a seven-day break after 9 April but opened the Nightingale Hospital in Birmingham by video on 16 April.
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Last week, William and Kate praised NHS workers for their “humility and compassion” at the Pride of Britain Awards.
The couple met six representatives of the NHS to present them with the award at one of Britain’s oldest hospitals, St Bartholomew’s in the City of London.
The duke said: “The devastating impact of the coronavirus pandemic has reminded us as a nation of how much we owe to the thousands of NHS workers who have gone far beyond the call of duty this year.
“They have worked tirelessly around the clock, with humility and compassion, in the most challenging of circumstances, putting their own lives on the line to help others.
“It is fitting that we are here today at Britain’s oldest hospital to thank and celebrate our NHS staff and to honour them with a Pride of Britain Award.”