President Donald Trump appeared to touch Queen Elizabeth II on the back during the State Banquet, which is a violation of royal protocol.
In order to touch the Queen, protocol dictates that she must first offer her hand to you.
The incident took place after Trump praised the Queen as a "great woman" for her work.
"From the Second World War to today, her majesty has stood as a constant symbol of these priceless traditions," Trump said of the Queen at the dinner.
"She has embodied the spirit of dignity, duty and patriotism that beats proudly in every British heart," he added.
It's not the first time the rule has been broken as former First Lady Michelle Obama did something similar.
Obama in 2009 went as far as to hug the Queen, which was described at the time as an "epic faux pas".
Describing the moment in her 2018 memoir, Becoming, the former first lady wrote, "Forget that she sometimes wore a diamond crown and that I'd flown to London on a presidential jet; we were two tired ladies oppressed by our shoes. I then did what's instinctive to me anytime I feel connected to a new person, which is to express my feelings outwardly. I laid a hand affectionately across her shoulder."
The Queen did not react in a noticeable way when Trump appeared to touch her on Monday.