The development comes nearly seven weeks after the palace announced that Prince Philip will retire from royal duties from September. At that time, the palace had also said that the royal will continue to attend previously scheduled engagements until August, with the monarch and individually.
The Duke of Edinburgh was admitted to King Edward VII Hospital in London last night, the palace said in a statement.
"Prince Philip is in good spirits and is disappointed to be missing the State Opening of Parliament and Royal Ascot," it said.
Yesterday, Prince Philip attended the Royal Ascot horse races, accompanying the Queen for a full day of activity.