Prince William's appearance at the Frankfurt Arena in Germany on Thursday comes the day before his 42nd birthday.
The future king, a passionate Aston Villa fan, presented shirts to the England men's squad before the team left for the tournament, making a surprise visit to St George's Park, England’s national football centre in Burton upon Trent.
He also shared his youngest son Prince Louis' advice, who suggested the players "eat twice the amount" to secure their bid for Euros glory.
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The Prince has been President of the Football Association since 2010.
England got off to a positive start in Germany when Jude Bellingham scored a header 13 minutes into their Group C opener against Serbia on 16 June.
See the best photos from the night…
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William's arrival
The Prince of Wales looked incredibly smart in a suit and tie as he headed to the match in Germany. Although Prince George is scheduled to appear at a future match, the young prince missed tonight's match, likely due to Friday being a school day.
2/11
Danish family
Frederik wasn't alone as he headed to the match, as he was joined by his youngest daughter, Princess Josephine, for the match.
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Royal greeting
Although rivals on the pitch, William and Frederik clearly weren't off the pitch, and they exchanged a friendly greeting when they crossed paths.
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Royal chats
The duo even had friendly conversations ahead of the match, with William pointing something out in the crowd.
5/11
National anthem
The Prince was seen singing the national anthem ahead of the match.
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Royal pals
Although the King and the Prince enjoyed a laugh ahead of the match, we imagine the mood was a bit frostier after England scored in the 18th minute.
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Princess Josephine steals the show
Frederik was a protective father of Josephine as the pair posed with William for photos.
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King Frederik smile
Frederik was able to steal back some happiness ahead of the second half when Denmark's Morten Hjulmand scored an equalizer in the 34th minute.
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Joy for Josephine
It wasn't just Frederik who was overjoyed with the goal, as Josephine was also seen getting excited next to her father.
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Disappointing result
The Prince of Wales couldn't help but show some of his disappointment as the game ended in a 1-1 draw, with a goalless second half.
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Sporting royals
Despite neither team emerging victorious, the royals were able to shake hands come the end of the match.
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