Some royal watchers raised questions over the president’s gesture yesterday (Picture: AFP via Getty Images)

Were you rubbing your eyes and blinking in disbelief when Joe Biden gently touched the King’s back on his visit to Windsor Castle yesterday?

To some, it was a blatant breach of protocol – you really shouldn’t initiate personal contact with a member of the royal family without them doing so first.

To others, it was just a friendly and unremarkable gesture between two men of a similar generation.

The contentious move came after Biden and King Charles met outside the Berkshire castle and enjoyed a short chat while shaking hands.

As they took a short walk together towards a platform where they were to listen to a band performing renditions of both the UK and US national anthems, Biden placed his hand on the monarch’s back.

Now, royal protocol is a murky business, and there is no official guidance on the royal family’s website regarding what you can and can’t do once you’ve been greeted.

Lucy Hume, the associate director at professional coaching company Debrett’s, previously told Reuters: ‘Best not to initiate personal physical contact with a member of the royal family.

‘Again, it may be that they offered to give you a hug or to put their arm around you, but usually wait and see what’s expected or what’s appropriate for the event.’

The incumbent US president is not the first to be accused of breaking such traditions – there was a fair amount of disgruntlement when Donald Trump walked a few steps ahead of the late Queen in 2018.

Biden did the same during yesterday’s meeting, but did the King mind?

A royal spokesperson didn’t exactly give the impression of barely concealed rage in their statement yesterday: ‘An extremely cordial and successful meeting that touched on a wide variety of issues of mutual interest and concern.

‘You will have seen for yourselves the personal warmth between His Majesty and the president.’

Buckingham Palace emphasised the warmth between the two men (Picture: Andrew Matthews/Getty Images)

And a Buckingham Palace source told CNN that King Charles, who is six years younger than the president, was ‘entirely comfortable with that kind of contact – and what a wonderful symbol of warmth and affection it was between both the individuals and their nations!’

Yesterday’s meeting came during Biden’s fleeting visit to London as he travelled to Vilnius in Lithuania for a NATO summit.

The president also spent time with Rishi Sunak in Downing Street during a packed day in the capital.

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We now know what the King thought of the president’s friendly gesture yesterday.