“But the training he is going to get in the run up to the big day is not snobbery – it will actually make him feel comfortable as it is designed to demystify Royal protocols and traditions so he will not be confused about how she act in front of royals.

“The etiquette lessons will cover everything from how he should act when he meets the Queen – by bowing his head and not touching her for example, and how he should start conversations with royals.

“He will also be taught the traditions of Royal weddings and how to eat the banquet that will be served as there will be a huge amount of cutlery and glasses involved at the meal.”

The source said knowing “the basics” of tradition helps put “outsiders” more at ease at Royal events.

"Ground rules” will also be laid down, such as advising Thomas not to drink too much at the wedding meal.

He is also likely to be firmly told to memorize protocols such as not talking to the Queen until he is spoken to, or turning his back on the monarch.

Prince Harry, 33, is still to meet his future father-in-law who US actress Meghan is said to “adore”.

Thomas married Doria in 1979. They divorced in 1988 and he now lives alone and is said to be “virtually reclusive”.

But he was recently spotted being measured up for his Royal Wedding suit by his local tailor in Rosarito, Mexico – a backstreet wedding and tuxedo shop minutes from his ocean-side home.

It is thought his specifications are being sent to a top tailor in London for the creation of a bespoke suit he will try and possibly get altered further when he arrives in the city.

Kensington Palace last week confirmed Meghan’s wedding will be “guided” by the type of traditions Thomas and his wife will be taught.

But a spokesman for the Palace added it would also contain touches “which reflects the personalities of Prince Harry and Ms. Markle – such as Meghan making a speech, which is not traditional form for a bride.

Meghan has already undergone months of etiquette coaching to prepare her for entry into ‘The Firm’.

She has displayed some of it by the way she sits with her legs crossed neatly at the ankle, knees pressed firmly together – a pose named the ‘Duchess Slant’.

Meghan will also already have been taught about banqueting with royalty, from how to hold cutlery to how the table is set and which utensils are used and when.

At her wedding, Meghan will first curtsy to her soon to be sister-in-law the Duchess of Cambridge.

According to the British Monarchy website, there are “no obligatory codes of behavior when meeting the Queen”, but it notes that many people prefer to “observe the traditional forms”.

For women that includes a small curtsy when meeting the monarch, while for the men it is a neck bow, from the head only.

On presentation to the Queen, the correct address is “Your Majesty”, followed subsequently by “Ma’am”, which should be pronounced with a short ‘a’, as in the word ‘jam’.

Other ‘do’s’ that should be noted include always taking the Queen’s lead by only speak when you are spoken to, and to not sit or begin to start eating until she has done so.

Arguably the most important thing to remember is that one should never touch the monarch, and only shake her hand if she offers it.

Taking photographs while visiting the Queen at home is also out, and guests should also never leave an event before a royal unless special permission has been granted.

One should also avoid any personal questions when conversing with royals – polite small talk will suffice.

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