The footballing legend and his second eldest son were beaming in the picture which was shared on social media but keen fans spotted the royals photobombing the snap.
The Beckhams shared the celebratory picture after watching England knock Germany out of the tournament with a 2-0 victory on Tuesday night.
David, 46, posted the photo with the comment: 'Special night last night at Wembley with fans back in the stadium watching the boys beat Germany .. Special to share this with one of my boys.'
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Fans have gone into a frenzy after spotting this selfie from David Beckham in which the Duke and Duchess of Cambridge have accidentally popped up in the background at Wembley
The retired footballer was seen chatting with William and Kate who attended with son George
They were accompanied in the Royal Box by the Duke and Duchess of Cambridge who had come along to show their support with son Prince George.
Prince William, who is president of the Football Association, was pictured chatting to David Beckham before kick off at Wembley Stadium.
The two families were seated in a star-studded Royal Box which also hosted pop stars Ed Sheeran and Ellie Goulding as well as former England keeper David Seamen.
While enjoying their quality time, David Beckham and 18-year-old Romeo looked dapper in suits as they watched the football.
David, 46, donned a charcoal grey ensemble with a navy and pink striped tie and a light grey shirt.
David Beckham enjoyed some quality time at the England v Germany match with son RomeoInsurance Loans Mortgage Attorney Credit Lawyer
Close: The pair looked