Prince William and Catherine mingled and chatted with guests throughout the event. But the princess also shared a poignant moment with former Met Police officer Tony Gledhill, a trustee of the VC and GC association, who clutched Catherine in comfort after telling her his wife of 67 years had recently died.

Mr Gledhill, a George Cross recipient, received words of support from the Waleses and the King and said afterwards: “The princess was lovely, she was fantastic.”

Now, former royal butler Grant Harrold, who worked for the Royal Family between 2004 and 2011, explained how Catherine was being the “perfect royal” in that situation.

Speaking on behalf of OLBG, he said: [Princess Catherine] is embracing the former officer back, which is quite sweet. But it is technically a breach of protocol.

“You’re not supposed to touch anyone in the Royal Family. [Catherine] is very calm and collected in her approach. She is being the perfect royal and just going with it.”

The etiquette expert added that the princess appeared “approachable” and explained why she didn’t pull away from the former officer when he embraced her.

He explained: “She has a very approachable and likeable way about her. Catherine is not going to turn around and say ‘You can’t do that’ and pull away from him. She is never rude.

“The palace advises you what you should and shouldn’t do in these situations. Catherine won’t hold him to that and he’s been given an award.

“The golden rule I always say is treat them like a fine object in a museum. You can look, you can admire, you can comment on - but never touch.”