The 31-year-old prince stuck out his tongue and made a funny face while Harlow, 21, chatted with her agent at the Audi Polo Challenge in London.
However, the model got the last laugh when she shared the pic on Instagram. “When you’re trying to have a serious convo but your agent and Prince Harry aren’t serious at all,” she captioned the shot, along with a laughing emoji and the hashtag “#photobomb.”
Harlow then posted a second photo with Prince Harry and Prince William in the background. She jokingly wrote, “Canadian girl on British territory (how did this photog get Prince Will & Harry in this shot!? Very cool.)”
Earlier in the day, the Duke of Cambridge, 33, busted out some yoga moves on the field at the polo match and proved that he’s superflexible — even while wearing a button-down shirt and white jeans.
This summer, the royal brothers are competing in a series of charity polo matches to raise money for 17 charities and good causes that they support.
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