The Queen was pictured using a walking stick for the first time in 17 years as she was accompanied by her daughter, the Princess Royal, to a service of Thanksgiving to mark the centenary of the Royal British Legion (RBL) at Westminster Abbey.
Her Majesty has previously been pictured with a walking aid in 2003 and 2004, following a knee operation.
In another departure, the 95-year-old monarch, who is the Legion's patron, arrived not by the traditional Great West Door to the abbey but via the Poet's Yard entrance, a shorter route to her seat.
Both developments are understood to be tailored for the Queen's comfort.
Buckingham Palace declined to comment, PA reports.
The Queen and Princess Anne, 71, joined the congregation representing those the RBL supports - serving members of the Armed Forces, veterans, and their families – alongside RBL members, supporters, staff and volunteers, as well as representatives from a range of community and partner organisations and government.
Tuesday marked the Queen and Princess Anne's first joint outing since Her Majesty's four-day tour of Scotland in June.
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The monarch looked elegant in a navy blue and matching coat hat for the service, along with a patterned dress. She accessorised with her signature patent loafers and Launer handbag.
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Meanwhile, the Princess Royal opted for a bold mauve ensemble, accessorising with a pearl necklace and a circular brooch.
The Royal British Legion has been celebrating its 100th anniversary throughout 2021 with a special programme of activity, paying tribute to those who have contributed to its proud history and celebrating with the communities across the UK and around the world who are at its heart.
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During the service, led by The Very Reverend Dr David Hoyle, Dean of Westminster, the Princess Royal gave a reading and the RBL's National President led the Act of Rededication, reaffirming RBL's commitment to its work and service.
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The Queen looked thrilled to have been given a bouquet of flowers following the service.
The Queen also accessorised with Queen Mary's Russian brooch, which contains a square sapphire and a diamond, surrounded by smaller diamonds. She inherited the jewels when her grandmother Queen Mary passed away in 1953.