"There were important things going on and I did not want to worry anyone," Prince William was quoted as saying by The Sun newspaper.
He was treated by palace doctors and followed government guidelines. He isolated himself at the family home Anmer Hall in Norfolk.
"William was hit pretty hard by the virus...At one stage, he was struggling to breathe," sources told the paper.
'Anyone can catch this awful disease'
"The Queen delivered her 'We Will Meet Again' address, and he just did not want to worry people...But as a result of his own experiences, he realizes (that) absolutely anyone can catch this awful disease - and knows how imperative it is that we all take this second lockdown seriously," sources further added.
England is set to enter a second national lockdown.
Though struck down, William continued work as usual
However, even after seeing the doctors and testing positive, William "was determined that it should be business as usual though."
"He was determined to fulfill his engagements," the publication quoted sources as saying.
Reportedly, the Duke of Cambridge carried out 14 telephone and video call engagements while in self-isolation during the month of April.
In UK, COVID-19 infected over a million
Before William fell ill, his father Prince Charles and UK's Prime Minister Boris Johnson -who had to be rushed to hospital - had also contracted the virus.
For the unversed, UK is one of the worst-hit countries from the COVID-19 pandemic. The disease has infected more than 10 lakh and claimed the lives of 46,717 there.