The decision to hospitalise him was taken following medical advice out of an “abundance of caution”.
His illness is not caused by the ongoing coronavirus pandemic.
On Wednesday campaign group Republic, which wants to replace the monarchy with an elected head of state, posted a video titled “It’s time” onto its YouTube channel.
The minute-long film, presented with dramatic music in the style of a movie trailer, has received over 1,000 views.
Prince Philip was taken to hospital as a “precautionary measure”
The Prince is being treated at London’s King Edward VII Hospital
The footage shows Prince Andrew, the subject of controversy over his relationship with convicted sex offender Jeffrey Epstein, and Prince Harry’s 2018 royal wedding, interspaced with captions promoting Republic.
They read: “In a country where royals reign one group will defy the odds to abolish the monarchy.
“A campaign will become a movement. It’s time.”
However, the video was condemned for the “bad timing” of its release by a leading royal expert.
Prince Philip’s condition is not coronavirus related
Speaking to MailOnline Richard Fitzwilliams said: “Bad material and bad ideas. With Prince Philip in hospital today, it’s bad timing too.”
He added: “Republic’s new publicity video ‘It’s Time’ is hilarious.
“It’s rather like a trailer for an extremely bad comedy as we see clips but only hear deafening music.
“Its Chief Executive Officer Graham Smith is shown speaking but we can’t hear a word of what he is saying.
“One group will defy the odds to abolish the monarchy”
“With Prince Philip in hospital today, it’s bad timing too”
“At the end, it actually says ‘starring the British people’ which is rubbish. According to YouGov they consistently have around 20 percent support’.”
The Queen and Duke of Edinburgh received coronavirus vaccines at Windsor Castle last month.
Due to their age, both royals were categorised as vulnerable and had been spending the lockdown in a protective ‘bubble’.
According to the BBC Prince Philip is expected to spend a few more days in hospital as he recuperates.
A YouGov poll found the Queen has a 74 percent approval rating
A 10 Downing Street spokesman said Boris Johnson had conveyed his “best wishes” to the senior royal.
Republic campaigns to replace the monarchy with an elected head of state.
It claims to have the backing of “over 80,000 republicans”.
The Queen is currently in isolation at Windsor Castle
On its website, the group states: “Republic is a membership-based pressure group campaigning for the abolition of the monarch and its replacement with a directly elected head of state.
“We represent all Britain’s republicans, bringing the case for a republic to a wider audience while scrutinising the actions of the royal household.”
A YouGov poll released last year found the Queen enjoys 74 percent public approval, ahead of William on 67 percent.
Source: EXPRESS CO UK