The Duke of Cambridge was struck down with coronavirus in April but kept the diagnosis secret so as not to “worry” anyone, it has emerged.
The Duke, 38, is said to have struggled to breathe during his illness and was treated by doctors before isolating at the family home, Anmer Hall, in Norfolk.
He is said to have later told one observer at an engagement: “There were important things going on and I didn’t want to worry anyone.”
The Duke’s diagnosis came shortly after it was announced that both his father, the Prince of Wales, and Boris Johnson had contracted the virus.
He was reportedly concerned that revealing his own plight to the nation would create further panic.
Kensington Palace sources played down the severity of his illness.
But a source told The Sun: “William was hit pretty hard by the virus – it really knocked him for six.
“At one stage he was struggling to breathe, so obviously everyone around him was pretty panicked.
“After seeing medics and testing positive – which was obviously quite a shock given how fit and healthy he is – William was determined it should be business as usual though.
“He was determined to fulfil his engagements.”
There was no public hint that the Duke had fallen ill during the height of the pandemic, not least as he continued to work throughout April, carrying out 14 telephone and video call engagements throughout the month.
Memorably, he was filmed standing at the door of Anmer Hall with the Duchess of Cambridge, 38, and their children, Prince George, seven, Princess Charlotte, five, and two-year-old Prince Louis as they lead the nation in a Clap for Carers.
Earlier that month he had told colleagues of consultant Amged El-Hawrani, 55, one of the first doctors to be killed by the virus, that he was “proud” of their work.
He had a seven-day break from calls and video messages from April 9 before opening the Nightingale Hospital Birmingham at the NEC via video link on April 16.
He told them it was a “wonderful example” of the “pulling together” happening across the country to fight the pandemic.
The source added: “The Queen delivered her ‘We Will Meet Again’ address and he just didn’t want to worry people.
“He felt there were more important things going on in the country.
“But as a result of his own experiences, he realises absolutely anyone can catch this awful disease – and knows how imperative it is that we all take this second lockdown seriously.”
Earlier this week, the Duke showed great empathy with Kate Garraway, a presenter on ITV’s Good Morning Britain, whose husband, Derek Draper, remains in hospital seven months after contracting coronavirus.
Both he and his wife, who were taking part in the Pride of Britain awards, told the broadcaster they wanted to give her “a hug” in the wake of her family’s ordeal.
The Cambridges said they had been touched by her experience, and how it had impacted their children Darcey, 14, and Billy, 11.
Prince Charles has spoken of his own brush with Covid-19, which saw him suffer a mild version of the illness and isolate at Birkhall, Scotland.
He said it had left him “even more determined to push and shout and prod” to rebuild the planet.
Meanwhile, the Prime Minister spent three nights in intensive care after being hospitalised on April 5.
Kensington Palace declined to comment.