Donald Trump appeared to breach royal protocol by touching Her Majesty on the back as she rose for his toast following his speech during the US State Banquet on Monday night.
The President, who had just referred to the Queen as a "great, great woman" in his speech, briefly and gently put his left hand out behind the monarch. The Queen, who was sat to his left, seemed unperturbed by the act.
Donald Trump delivered a glowing tribute to his host ahead of their sit down dinner.
He began by thanking the monarch for the "warm welcome" and "beautiful weather". "Your majesty, Melania and I are profoundly honoured to be your guests for this historic state visit. Thank you for your warm welcome, for this beautiful weather, your gracious hospitality, and Your Majesty's nearly seven decades of treasured friendship with the United States of America," he said.
POTUS also paid tribute to Prince Philip, who was absent from the engagement, for his "distinguished and valiant service in the Royal Navy during the Second World War."
It was a family affair for the President and First Lady Melania at the white tie and tiara event as they were joined by four of Mr Trump's five children - Ivanka Trump, with her husband Jared Kushner, Donald Trump Jr, Eric Trump and his wife Lara, and Tiffany Trump.
Following the glittering banquet, Ivanka shared images of her family at Buckingham Palace, tweeting: "Beyond wonderful to share this unforgettable evening with this crew."