The Princess Royal was joined by her husband, Vice Admiral Sir Timothy Laurence, for a rare joint outing on Saturday.
On Monday, Buckingham Palace shared a photo on the Queen's Instagram account from the couple's engagement, saying: "On Saturday The Princess Royal and Vice Admiral Sir Tim Laurence attended the national #ArmedForcesDay celebrations at the National Memorial Arboretum.
"The Princess had the chance to personally thank members of the Armed Forces community, including military families, for their service."
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Both Anne and Sir Tim were dressed in their naval uniforms, with their medals proudly on display.
The couple, who have been married since 1992, were pictured smiling as they met personnel and their families at the event, which included a flypast by the Red Arrows.
The royal family shared this photo of Princess Anne and Sir Tim
Armed Forces Day in the UK is an annual event celebrated in late June to commemorate the service of men and women in the British Armed Forces.
The Prince of Wales and the Duchess of Cornwall also shared their support on the day, tweeting: "Since the start of the pandemic, our Armed Forces have been there to help the nation through the difficult times, from setting up Covid-19 testing sites to supporting the NHS by assisting ambulance workers. Thank you all for your service."
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Princess Anne wore her naval uniform and medals
This week, the Princess Royal, 70, will join the Queen in Scotland to mark Royal Week.
Her Majesty will undertake a range of engagements celebrating Scottish community, innovation and history during her four-day visit. The monarch, 95, will be joined by Prince William, known as the Earl of Strathearn in Scotland, for the first day of her visit on 28 June, and by Princess Anne for outings on Wednesday 30 June and Thursday 1 July.
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