On Wednesday, after Mr Biden was sworn-in, he visited Arlington National Cemetery in Virginia to lay a wreath at the Tomb of the Unknown Soldier.
During the visit, the president spoke with Bill and Hillary Clinton, with Jon Davidson, a staff member of the former president, sharing a photo of the moment on Twitter.
“It’s a new day in America,” Davidson captioned the photo, which was taken in the Memorial Display Room at Arlington National Cemetery.
However, upon zooming in, viewers noticed that, in addition to the US presidents, the picture also featured a portrait of Prince Harry dressed in his British Army uniform in the backdrop.
“That’s an impressively large image of Prince Harry top right…” royal reporter Victoria Arbiter tweeted in response to the photo, prompting others to share their own amused reactions to the royal cameo.
“How bizarre is that! Haha good catch!” one person tweeted in response, while another said: “Love this. Great to see Prince Harry’s presence.”
The photo of Prince Harry is reportedly from the royal’s visit to Arlington National Cemetery in 2013, when he took part in a wreath-laying ceremony.
During his visit, the duke, who served in the British army for 10 years, also left flowers at the memorial to President John F Kennedy and a handwritten note on a soldier’s grave.
The note read: “To my comrades-in-arms of the United States of America, who have paid the ultimate sacrifice in the cause of freedom,” and was signed: “Captain Harry Wales,” according to Today, which notes Harry wore his full British ceremonial uniform for the visit.
While Prince Harry, who lives in California with wife Meghan Markle and son Archie, was not actually in attendance at the inauguration, he and President Biden have met before. In 2016 and 2017, Mr Biden and Dr Jill Biden attended the duke’s Invictus Games.