The Queen is intending to attend a service of thanksgiving for the Duke of Edinburgh later, Buckingham Palace has said.
Other senior members of the Royal Family will also be at the memorial at Westminster Abbey for Prince Philip, who died last year aged 99.
The service will celebrate his public service and a "long life lived fully".
Representatives of his charities, including the Duke of Edinburgh's Award, will be in the congregation.
It will be the first public event, outside of her own residences, attended by the 95-year-old monarch this year,who will travel down to London from Windsor Castle.
The Queen has had problems with her mobility and had to pull out of the Commonwealth Service earlier this month.
Buckingham Palace earlier indicated a decision on the day would be taken as to whether or not she would attend.
Special measures have been put in place for her comfort, including keeping the length of the service to 45 minutes. She is also expected to enter through the back of the Abbey via Poet's Corner, as this is a shorter route to her seat.
Other senior members of the Royal Family - including Prince Charles and Camilla, and Prince William and Catherine - are set to attend the service, which starts at 11:30 BST. It will be screened on BBC One, with coverage starting at 10:30.
The thanksgiving service will hear the Dean of Westminster, David Hoyle, offer prayers for a "man of rare ability and distinction" who "put privilege to work and understood his rank as a spur to service".
It is also expected to be the first public appearance of Prince Andrew, the Duke of York, since the settlement of a civil sex assault case in the US.
But Prince Harry, who has been in a legal dispute over the provision of security, has not travelled from California, where he lives.
Prince Philip died last April, during Covid regulations that restricted gatherings including funerals and memorials.
Keeping to the rules meant that his funeral had to be limited to 30 guests, producing a memorable image of the Queen sitting alone.
So this service will include elements that had been planned for Prince Philip's funeral, such as the entry to Westminster Abbey being lined by Duke of Edinburgh gold award winners.
The hymn Guide me, O thou great redeemer, also intended for the funeral, will be sung, along with music by Beethoven, JS Bach, Wagner, Vaughan Williams and William Byrd.
The Queen and Prince Philip had been married for 73 years and in her Christmas message the Queen spoke in unusually personal terms about the loss of her "beloved" Philip.
Wearing a brooch she had worn on their honeymoon, she remembered her "irrepressible" husband and his "capacity to squeeze fun out of any situation".
The service will reflect the duke's life, work and enthusiasms, with the congregation including representatives of some of the 700 charitable organisations that he supported.
They will range from the Outward Bound Trust and Voluntary Services Overseas to the Caravan and Motorhome Club.
Many charities had a focus on inspiring young people and giving them wider opportunities. There was also an emphasis on conservation and protecting the environment.
Environmental campaigner and broadcaster Sir David Attenborough is expected to be among the guests, along with political leaders.
Prince Philip's love of the sea and his links with the Armed Forces will be heard in the music of the Royal Marines band, which will conclude with a piece called The Seafarers.
The flowers on display will include orchids, a reference to the orchids in the Queen's wedding bouquet.
She and Prince Philip were married in 1947 at Westminster Abbey, where her coronation was later held, and now where she will attend her husband's memorial.