Donald Trump reportedly broke Royal protocol just seconds after touching down at Windsor Castle.

The US President has begun his three-day trip to the UK, with his first full day now being carried out. He was formally greeted by the Prince and Princess of Wales the minute he stepped off his Marine One helicopter.

Kate and William gave Donald and Melania Trump a warm welcome, but one royal expert has shared Mr Trump may have carried out a faux pas while shaking hands with the future King.

During the handshake, the President appeared to go one step further than a simple handshake, by bringing his left arm up to tap William on the shoulder as the gesture came to an end.

READ MORE: Everything we know about Donald Trump's lavish state banquet as US president arrives at Windsor Castle

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