Prince Harry attended a Remembrance service organised by Brackley Town Council, while other members of the Royal Family were carrying out official engagements in London.
According to witnesses, the Duke of Sussex avoided attracting attention, choosing instead to stand quietly among members of the public on a side street.
In a video sent to news agency SWNS, Harry can be seen wearing his military medals and a poppy while standing beside The Crown Hotel.
Prince Harry and Meghan returned to the UK over the summer and have reportedly been staying at a private estate in Croughton, Northamptonshire.
An onlooker at the Brackley service told SWNS: “He was at the memorial service – he was stood next to the pub.
“He was stood there watching and then afterwards he went into the market and started shaking everyone's hand.
“He was there for the whole service – we were there for 20 or 30 minutes, and he was there before us.
“He just wanted to show some respect. It is a shame. At the end of the day he’s served so why can’t he show his respects.”
Prince Harry served in the British Army for more than 10 years, reaching the rank of Captain and undertaking two tours of Afghanistan.
In 2014, he founded the Invictus Games, an international sporting event for wounded, injured and sick serving military personnel and veterans.
9. Prince Harry at Brackley Remembrance Sunday Service
Brackley Brass Band performed at the Brackley Remembrance Sunday Service. (Richard Watt) Photo: Richard Watt
10. Prince Harry at Brackley Remembrance Sunday Service
Archie Batty, the musical director at Brackley Brass band (Richard Watt). Photo: Richard Watt
11. Prince Harry at Brackley Remembrance Sunday Service
An officer of the US Armed forces from nearby RAF Croughton at the service. (Richard Watt) Photo: Richard Watt
12. Prince Harry at Brackley Remembrance Sunday Service
An female Army cadet salutes after presenting her wreath (Richard Watt). Photo: Richard Watt