The King and Queen are due to attend a Christmas Day church service in Sandringham alongside the Prince and Princess of Wales plus other royals.
It was announced last week that the Duke of York would not attend the annual gathering after an alleged Chinese spy, named following a High Court judgement, was found to have been linked to the prince.
Wednesday’s service will take place hours before the King’s Christmas message airs – it will be delivered from a former hospital chapel, in a year that has seen the monarch undergo cancer treatment.
His daughter-in-law Catherine, expected to be at the service, recently marked her biggest return to royal duties after finishing chemotherapy.
The pair announced their cancer diagnoses within weeks of each other – the King in February of this year and Catherine the following month.
A crowd of people has already started gathering outside St Mary Magdalene Church, in Sandringham, as they hope to catch a glimpse of the royals before or after the late morning service.
The royals will then spend Christmas at their Sandringham estate, in Norfolk, which has been the customary seasonal meeting place for the family since 1988.
Prince Andrew’s absence was confirmed after Yang Tengbo, also known as Chris Yang, was named as being an alleged Chinese spy who had been banned from entering the UK.
The man, reported to have been part of an operation to get close to figures of influence, was described by judges of the Special Immigration Appeals Commission court as having an “unusual degree of trust” with the prince.
Prince Andrew’s office said nothing sensitive had ever been discussed with Mr Yang.
The prince is seldom seen in public since apologising for his links to convicted sex offender Jeffrey Epstein, and no longer takes part in frontline royal duties.
Meanwhile, the monarch’s traditional speech, recorded earlier this month, will be broadcast as usual on television and radio at 15:00 GMT.
It was recorded in the Fitzrovia Chapel, central London. It is the first time in more than a decade that the Christmas message has been recorded from a place that is not in a royal palace or estate.
The location suggests that healthcare and supporting community links could be themes for the annual speech.
Both the King and Catherine have spoken about their cancer journeys, with the former’s treatment sessions continuing.
Kensington Palace released a video in September showing Catherine announcing that she had completed her chemotherapy treatment, and promoted the message that “out of darkness can come light”.
Earlier this month, she hosted a carol service at Westminster Abbey alongside Lady Gabriella Windsor, the King’s second cousin.
The event was dedicated to individuals who have shown love, kindness and empathy to their communities.