Mr Trump and the First Lady were greeted by the Prince of Wales and Duchess of Cornwall as they stepped from the Marine One helicopter in the grounds of Buckingham palace shortly after midday on June 3.
The pair were then taken to meet the Queen – their second introduction following Mr Trump’s working visit to Britain last summer.
However, just a few hours in to his trip and Mr Trump has already been slammed for not bowing to Her Majesty. Instead, he opted or a handshake.
"Did...did that man just fist-bump our Sovereign? Get him on the block," one person wrote on Twitter.
While some royal fans were horrified by such an act, there is "no obligatory codes of behaviour when meeting the Queen or a member of the royal family, but many people wish to observe the traditional forms."
According to guideline notes shared on the royal family's official website: "For men, this is a neck bow (from the head only) whilst women do a small curtsy. Other people prefer simply to shake hands in the usual way."
Meanwhile, it is understood a huge security operation is in place for the duration of Mr Trump's visit.
In fact, police officers could be seen standing at three different points on the roof at the front of the Buckingham palace as he and his wife arrived.