When have the Queen and Prince William carried out royal engagements?
Watch: Queen carries out first engagement outside palaces
The Queen’s joint engagement with her grandson Prince William is a rare cross-generational visit in the royal books.
While they are both senior royals, the pairing is an uncommon sight, as William tends to carry out engagements either alone or with his wife, the Duchess of Cambridge.
However, they have worked together at Buckingham Palace, in more diplomatic settings, when the Queen is playing host to a leader from another nation.
They last carried out work together without other members of the Royal Family in June 2019, as they received the Governor General of Australia in an audience at Buckingham Palace.
They also went to church together in Balmoral in September 2019, though this was not an official engagement or meeting.
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In 2017, they were seen together on several occasions. William accompanied his grandmother to church in Scotland, leaving then pregnant Kate at home, over the Christmas break in Balmoral.
In the same year, he helped her host then president of Germany Frank-Walter Steinmeier and his wife Elke Budenbender, again at Buckingham Palace.
He also went with her to visit the scene of the Grenfell Tower fire in West London.
In 2016, the Queen and Prince Philip visited the East Anglian Air Ambulance site where William was working, and he greeted them during their tour of the site.
The Queen and Philip visited William at RAF Valley in Anglesey, Wales, when he was based there in 2011.
And William couldn’t help getting the giggles in 2006 when his grandmother carried out the inspection at Sandhurst, the military academy.
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The Queen used to carry out most of her engagements with her husband, the Duke of Edinburgh. He retired in 2017, and she attends many engagements on her own now.
But she is also keen to ensure she gives the seal of approval to new members of the Royal Family, and took Meghan, the Duchess of Sussex, on a trip with her to Chester shortly after her wedding to Harry in 2018.
She’s also carried out engagements with Kate.
During lockdown, she carried out a zoom virtual engagement with her daughter, Princess Anne, but it could be a significant move that she asked her grandson William to join her for the first in-person engagement.
Ingrid Seward, royal biographer, told Yahoo UK: “I think the Queen feels she needs to be seen to lift people’s spirits and what better way than with her grandson by her socially distanced side to show her respect for all he is doing.”
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The visit to Porton Down on Thursday saw the Queen and the prince meet military personnel and scientists who were involved with the response and clean-up in Salisbury after the 2018 Novichok poisoning.
William presented the Firmin Sword of Peace to some members of the 102 Logistic Brigade who helped with the incident after former spy Sergei Skripal and his daughter Yulia were targeted with the nerve agent.
And the Queen unveiled a plaque as she formally opened the new Energetics Analysis Centre at the Wiltshire site.
Watch: William and the Queen carry out joint engagement in 2017