The Duke of Edinburgh has been hospitalised in London with an infection.
The 96-year-old will miss out on supporting Queen Elizabeth at the State Opening of Parliament, which has just commenced at the House of Lords in the British capital.
Prince Charles will step in on behalf of his father as Her Majesty delivers her annual Queen's speech.
A statement from Buckingham Palace explained: "The Duke of Edinburgh was admitted to King Edward VII Hospital in London last night, as a precautionary measure, for treatment of an infection arising from a pre-existing condition."
It concluded: "Prince Philip is in good spirits and is disappointed to be missing the State Opening of Parliament and Royal Ascot. The Prince of Wales will accompany The Queen to the State Opening. Her Majesty is being kept informed and will attend Royal Ascot as planned this afternoon."
While the palace wouldn't confirm his exact medical illness, royal insiders have told the UK press that the father-of-four is "up and about and is in good spirits.”
In May, it was confirmed The Queen's right-hand man was stepping down from his royal duties.
In a statement, the palace said that Philip would not be accepting new invitations for visits and engagements, although "he may still choose to attend certain public events from time to time."
The Duke is considered one of the hardest-working royals and conducted 110 days of appearances last year - outnumbering several young family members, including Prince William.
Dubbed "the original James Bond", the Duke has had good health over the years but was hospitalised in 2012 during the Queen's Diamond Jubilee from a bladder infection.
In 2011, he underwent treatment for a blocked coronary artery and over the most recent Christmas holidays, he and The Queen suffered heavy colds.
Since his retirement, Prince Philip has been spotted on several occasions carriage racing.
His last public appearances were at Royal Ascot on Tuesday and Trooping the Colour on Saturday.
Wishing the Duke a very speedy recovery!