Taking to Twitter on Monday, the royal commentator lashed out against Kensington Palace, questioning how people are supposed to trust the monarchy moving forward.
“Prince William’s decision to LIE about contracting COVID-19 earlier - for whatever reason - is appalling,” Robert wrote.
“KP were are asked several times by the media whether Prince William had contracted the virus and were told categorically ‘no’. This has created a serious issue of trust.”
“If the palace is prepared to LIE about an issue as serious as Prince William, second in line to the throne, contracting COVID-19 what else have they LIED about when questioned by the press and why should the media believe any denials going forward? This raises serious issues.”
When Robert suggested that William’s decision to lie had created a problem of trust going forward, ITV NEWS Royal Editor Chris Ship weighed in on the conversation.
“It seems Kate, the Duchess of Cambridge and Prince George, Princess Charlotte and Prince Louis did not contract #coronavirus - even though William had,” Chris began.
“Although given [William] kept his diagnosis secret for six months - we’ll have to take their word for it,” he added.
Daily Express royal correspondent Richard Palmer also shared a comment, which echoed both Robert and Chris' concerns.
“If the future King contracts a potentially fatal virus that the entire world is worried about during a lockdown and he and those around him cover it up, that raises serious questions about whether we can trust anything he or his advisers say,” Richard wrote.
Canadian royal expert Patricia Treble responded to Richard’s tweet, writing: "Cover-ups are always more damaging than the original act.
"That a serious illness of the second in line to the throne is kept secret until a journalist breaks the story six months later feels like questionable judgment and advice," she wrote.
William underwent treatment for COVID-19 at his family home Anmer Hall, in Norfolk, where he remained and isolated according to government guidelines, according to The Sun.
A source reportedly claimed to the publication that William was struck down "pretty hard" by the virus, and at one point he allegedly suffered breathing difficulties.
"At one stage he was struggling to breathe, so obviously everyone around him was pretty panicked," the source alleged.
But despite his shock diagnosis, the prince was reportedly able to carry on with his regal duties, while undergoing treatment at his Norfolk home.
"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," the source claimed.