Ahead of the service, her former husband, Prince Andrew, was spotted travelling with the Queen while his daughters Princess Beatrice and Princess Eugenie walked inside with their respective spouses, Edoardo Mapelli Mozzi and Jack Brooksbank.
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It is likely that Sarah remained at the family home, Royal Lodge in Windsor, which she stills shares with Andrew, and will spend the day looking after her grandchildren, August and Sienna.
The Queen made the journey from Windsor to London to attend the high profile and personally significant occasion in honour of her late beloved husband, who died in April last year.
She was joined by more than 30 foreign royals, the Duke's wider family and friends, and 500 representatives from his patronages and charities. However, the Duke and Duchess of Sussex recently confirmed that they would not be returning from the US for the event.
Sarah did not attend the ceremony on Tuesday
The ceremony marks the first time the Duke and Duchess of Cambridge have been seen since their royal tour of the Caribbean last week.
Meanwhile, the service will pay tribute to the Duke of Edinburgh's dedication to "family, nation and Commonwealth", his contribution to public life and his steadfast support to his charities. It will also incorporate some elements planned for the late royal's funeral, which were unable to go ahead due to COVID-19 restrictions in place at the time.
This includes Gold Award Holders from The Duke of Edinburgh's Award, and representatives from UK Cadet Force Associations, step lining the entry routes into Westminster Abbey for members of the royal family and other guests.
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