Princess Anne (floral dress, shaded blazer) doesn't stand within the receiving line for Trump and Melania, nonetheless stands off to the facet whispering about it and when the Queen appears over to place a query to her about it she true shrugs.
The short video clip immediately went viral and started to trend on Twitter.
Princess Anne speaking with Angela Merkel at the North Atlantic Treaty Organisation summit. No, she didn't snub the Trumps. But there wasn't anyone waiting: Trump was the last leader to be received by the Queen.
Queen: "Anne, get over here right this instant".
However, according to The Times journalist Valentine Low, who was at the event, a mix-up by the Queen had caused the headline-making moment.
Someone else put: "Princess Anne is the one member of the Windsor family I admire for having principles".
The 93-year-old monarch then looks over, apparently to check which world leader she is due to receive next, before noticing her daughter standing in the background by the door.
Much of the conversation is inaudible, but it happened after Trump finished an unusually long press event alongside French President Emmanuel Macron.
To the left of the screen, Princess Anne hovers in a doorway watching the greetings.
He said the Queen's gesture to her girl was "charming".
As fans of "The Crown" television series will know, Anne is known as the queen's most down-to-earth child - she notably didn't give her children royal titles.
Anne is the queen and Prince Philip's second child and only daughter. She is often dubbed the "hardest-working royal" by the British press for taking part in more royal "engagements" than any other member of the royal family.
Macron then replies although is comments are inaudible, before Trudeau says: "you just watched his team's jaws drop to the floor".