The Princess of Wales is recovering in hospital after undergoing surgery, and King Charles III is set to undergo a medical procedure next week.
Catherine will step back from royal duties for months after surgery for an unspecified but non-cancer-related abdominal condition.
The King’s benign prostate condition will be treated next week.
The unexpected health announcements were made within two hours of each other on Wednesday afternoon.
Details about the health of senior royals are usually a closely guarded secret and only announced to the public in limited circumstances, so the decision to release two significant updates in one day was striking.
At about 14:00 GMT, Kensington Palace disclosed the princess was admitted to a private hospital in central London on Tuesday for a procedure and is recovering there.
It is understood the princess is doing well but is expected to spend up to two weeks in hospital and be out of the public eye until after Easter as she continues a months-long recovery.
It is clear from the length of time she needs to recuperate and the tone of the statement from the palace that her condition is serious, though it was stressed the procedure had been planned and successful.
The palace called for the princess’ medical privacy to be respected, adding: “She hopes that the public will understand her desire to maintain as much normality for her children as possible.”
The Prince of Wales will also step back from royal duties in the coming weeks to be with his wife and Prince George, 10, Princess Charlotte, eight, and Prince Louis, five.
Less than 90 minutes later, a separate statement was published by Buckingham Palace revealing the King requires a “corrective procedure” next week for an enlarged prostate.
The condition is common in older men and is not cancerous. The King turned 75 in November.
It is not known what procedure the King requires, but the palace said his “engagements will be postponed for a short period of recuperation”.
His treatment is not a sufficient disruption to trigger any of the constitutional mechanisms for when the head of state is seriously ill.
In such circumstances, “counsellors of state” can act as stand-ins for the monarch and carry out duties such as signing official documents – but Buckingham Palace has said that will not be necessary.
The King is staying at his private home near Balmoral with the Queen, and royal sources said he was in “good form” and in “good spirits”.
The timing of the announcement about the King so soon after the news about the princess is thought to have been unavoidable due to the monarch’s scheduled engagements on Thursday and Friday.
He had been due to meet with foreign dignitaries and Cabinet members in Scotland, so the news had to be made public as those meetings were cancelled on doctor’s advice.
A new openness?
Medical issues for the royals have been kept very private in the past – and the announcements about the King and the Princess of Wales might seem to show a greater degree of openness.
It is understood the King wants his own experience of getting prostate treatment to help raise awareness and to encourage others to have checks.
For the princess, although there are no explicit details about the surgery, there is much more information from the palace than in previous years, with a reassurance her illness is not cancer-related, that it was not an emergency operation and a clear sense of how long the recuperation will take.
But much of this frankness might also have been necessary to get ahead of the news narrative, as questions would inevitably have arisen if the King and the princess began to cancel planned events.
There had been talk of overseas trips for Kate and William in the spring and there would have been pressure to confirm this.
Now the health issues have been revealed, the royals will hope for some more understanding about why the King and the Prince and Princess of Wales are temporarily not carrying out public duties.