The Duchess of Sussex is joining the Queen on board the Royal Train this evening for their overnight journey to Cheshire.
Meghan, who is performing her first engagement without Prince Harry tomorrow, is leaving her husband for the first time since their wedding in May.
The monarch has invited Meghan to accompany her for a day of engagements on Thursday and MailOnline understands that, given the distances involved, the train will set off on Wednesday, arriving at Runcorn Station on Thursday morning.
While the Queen always tends to make long distance journeys on her train overnight, it will be quite the eye-opener for her new grand-daughter-in-law.
The locomotive consists of nine carriages in total, however, these are often reduced to seven depending on the number of people travelling, and Her Majesty is said to described it as one of the few places where she can relax in total privacy.
At over 150 years old it is the only private, non-commercial train service catering to one family still in operation in the UK and these photos offer a rare glimpse into Britain's most exclusive railway service.
Much of the nine-carriage train currently in service dates back to 1977 when it was extensively used during the Silver Jubilee tours and while a novel experience, it is terribly dated and not entirely luxurious.
In fact, photographs of inside the train show how it is now a lot more functional, in contrast to the plush interiors that it used to boast in its glamorous heyday.
This comes after criticism over the expense of the royal train, which cost British taxpayers £900,000 in 2016.
Her Majesty's personal saloon is 75ft long and fitted with secondary air suspension giving passengers an exceptionally smooth and comfortable ride.
It has a bedroom, decorated in light pastel shades, with a 3ft-wide single bed in one corner (there are no double beds on the Royal Train) made up with cotton sheets and woollen blankets.
While Prince Philip's pillows are plain, the Queen's are trimmed with lace, with a small Royal cipher in one corner. The ceiling has subdued strip lighting and there are several reading lamps near the bed.
The adjoining bathroom has a full-size bath, but the fittings are modest and functional.
The train operators make sure the carriages are not crossing any bumpy points just after 7.30am: that could make the water slop around when the Queen is taking her bath. The train's speed is always lower than the normal maximum for any route.
The sitting room has a sofa with hand-stitched velvet cushions, armchairs and the small dining table where the Queen and Prince Philip have breakfast.
The table can be extended to seat six people. There is also a desk in one corner where Her Majesty works on her official papers.
Although she has enjoyed several meetings with the Queen and spent time with her at Windsor Castle, the overnight journey will be unprecedented for Meghan.
The King's favourite was his smoking room, which was manned by two liveried footmen, one just to light His Majesty's cigars and the other to adjust the curtains and windows in case the sunlight was too strong, or fresh air was required.
His son and successor, George V, had the distinction of installing the first bath on a train anywhere in the world.
While Queen Victoria's was the first train in the world to have a lavatory installed on board - in 1850, at the suggestion of Prince Albert - only the Prince Consort used it in the early days of Royal progress. Members of the entourage who invariably accompanied the Queen had to wait until the train stopped and then use public lavatories.
While the train is fitted with several sleeper carriages the locomotive never travels through the night, instead making stops at secret locations away from the mainline so that the royal passengers can sleep uninterrupted.
The overnight stops are usually made about an hour's travelling time from the final destination. This means the Royals are able to rise, bathe, dress, have a leisurely breakfast and then be briefed by their private secretary on the day's programme as the train completes its journey. Arrivals are usually timed so that they do not disrupt any normal rail schedules.
The appearance of the Queen's current saloon is a long way from the velvet interiors and plush furnishings of carriages of the Victorian era.