“Harry is very close to his brother and his sister-in-law, and presumably by extension, Meghan is also part of that circle,” Hanson explained. As far as the wedding is concerned, Harry “would not want something to upstage, nor to prohibit such a major guest from coming.

“I think they have planned it nicely (their engagement was announced in November 2017) as they knew the royal baby was coming and therefore the wedding was put after that,” he said.

Hanson, who has been teaching royal etiquette for the last 12 years, half-jokingly said “This wedding is probably going to be the one wedding that irritates everybody likes me, because actually it will break the protocol as Meghan seems to have her own take on what she wants to do.”

The wedding cake has been announced well in advance, and the photographer as well as the florist are usually not revealed until much closer to the event, if not on the day or after the day, he added, “so already we are beginning to see, on smaller levels, a different sort of thing.”

Hanson said Harry, who achieved the rank of captain in his 10 years of Army service, is likely to wear morning dress at the wedding, instead of the military uniform the Duke of Cambridge wore at his big day, because the upcoming wedding is less formal.

According to Hanson, for men, key morning dress rules include a black or dark grey tailcoat with neck tie, and the waistcoat is usually double-breasted. For women, it will be a formal dress with jacket over the top, hats instead of headpieces, plus gloves to be super-correct.

When asked how much Markle’s previous marriage and divorce matter to the royal court, Hanson said it would have been more of an issue if Harry were directly in line to the throne, although the royal family has relaxed their attitude to divorce during the Queen's reign.