Queen Camilla has pulled out of a number of scheduled engagements this week due to a chest infection, Buckingham Palace has said.
No further details regarding her illness or treatment have been released but she is understood to be resting at home under doctors' supervision.
The Duchess of Gloucester will step in on behalf of the Queen, 77, at the annual opening of the Field of Remembrance at Westminster Abbey on Thursday.
A statement from the Palace said the Queen hopes to recover in time to attend this weekend’s Remembrance events.
Senior royals ordinarily attend a number of Remembrance events.
The Queen will also not attend a Buckingham Palace reception for Olympic and Paralympic athletes, which will be hosted King Charles III, later that evening.
The statement from the Palace read: "Her Majesty The Queen is currently unwell with a chest infection, for which her doctors have advised a short period of rest.
"With great regret, Her Majesty has therefore had to withdraw from her engagements for this week, but she very much hopes to be recovered in time to attend this weekend’s Remembrance events as normal."
The Queen and King recently returned from a royal tour in Australia and Samoa.
King Charles is being treated for an undisclosed form of cancer and postponed public-facing engagements in February, before resuming public events in April.
