Victoria: Who was the real Harriet Duchess of Sutherland – and did she fall in love with Prince Ernst?

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"The last time we saw her she was waiting in a corridor thinking that Ernest is going to come and propose to her," Clunie tells RadioTimes.com. "He is not only a no show, but sends [servant] Brodie along with minimal explanation, Obviously Harriet is once again completely broken-hearted. Sometimes I can't believe she keeps going back!"

The Christmas special is a "weird" time for Harriet. As snow piles up outside and Prince Albert leaps around merrily decorating the palace with fir trees and baubles, Ernest is summoned back to England to celebrate the festive season with his brother's family. That means he's thrown back together with the woman he rejected so harshly. She's extremely angry at him, but still very much in love. So she makes a grand and risky gesture to demonstrate how much she wants him – "and then once again he completely breaks her heart."

Poor Harriet! She still doesn't know the truth that Ernest has been hiding: his venereal disease and the syphilitic rash that decorates his torso and causes him such shame. Will he finally admit the truth?

Did Prince Ernest and Harriet Duchess of Sutherland have a relationship in real life – and did they marry?

"We don't even think they really met in real life," Clunie laughs. "I think they were probably in the same room at the same time but I think she was about 20 years older than him.

"And hilariously in real life, Harriet Sutherland had a famously happy marriage with the Duke of Sutherland and they had these 11 children and lived happily ever after. So we have slightly deviated away from the truth. But it's all for good telly."

Who was Harriet, Duchess of Sutherland?

Harriet's full title was (deep breath) Harriet Elizabeth Georgiana Sutherland-Leveson-Gower, Duchess of Sutherland, and she was a great friend of Queen Victoria's from the start of the monarch's reign until her own death 30 years later. She was married to an extremely wealthy Whig MP, but became an important figure in London high society in her own right and served as Mistress of the Robes under several Whig administrations.

As the third daughter of George Howard the Earl of Carlisle and his wife Lady Georgiana Cavendish, Harriet – who was 13 years older than the Queen – was born into one of the most prominent Whig families of the early 19th century. At the age of 17 she married her cousin Earl Gower (aka the Duke of Sutherland), an MP who had been elected for a "rotten borough" in Cornwall.

He was two decades her senior, but the Sutherlands shared a very affectionate marriage and produced an impressive 11 kids: four sons and seven daughters. ITV's Victoria may have killed off Harriet's husband in the 1840s but he actually stuck around for a couple more decades, living until the ripe old age of 75.

Harriet and the Queen shared an enduring friendship. After Albert's death, Victoria spent the first weeks of her widowhood with the Duchess as her only companion. Harriet's own beloved husband had died earlier that year and they must have had a lot in common in their grief.

A cheerful and charming woman, Harriet became a renowned philanthropist and political hostess. She was extremely interested in politics – probably more than her MP husband – and pioneered the use of the "country house weekend" for public figures to gather for friendly discussions and debate.

Making use of her importance in the London social scene, Harriet also led a movement to rally English women against the American slavery. However, her anti-slavery campaign was controversial as the Sutherlands' own tenants in the Scottish highlands lived in poverty.

Only two years after her husband's death, Harriet was struck down by illness. She died in 1868 at the age of 62.

Who was Albert's brother Prince Ernst?

As little boys, Ernst and Albert were brought up like twins with a close bond that was only strengthened by their family troubles. According to their childhood tutor, "they went hand-in-hand in all things, whether at work or at play. Engaging in the same pursuits, sharing the same joys and the same sorrows, they were bound to each other by no common feelings of mutual love."

The two German princes had to endure their parents' separation and divorce and their mother's banishment: they never saw her again before her death, which came only a few years later. Their father the Duke of Saxe-Coburg and Gotha had endless affairs and liaisons, barely pausing to marry his sister's daughter the Duchess Marie who became the boys' stepmother (as well as their first cousin). All in all it was a weird childhood.

Ernest and Albert first visited their "eligible" cousin Victoria in 1836. She found Ernest lively and sociable with a love of gossip and also approved of Albert, but – despite the hopes of the boys' families – no marriage proposal for either Prince was forthcoming. So off they went back to the continent. Ernst trained in the military and both brothers then went to the University of Bonn, before setting off on a trip around Europe.

In 1839 they went back to England to visit Victoria, who had now become Queen. It was Albert who caught her eye and five days later she proposed.

Ernst now needed to marry and advance the family name, just like his brother.

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Who did Ernst marry in real life – and did he have syphilis?

Ernst suffered from venereal disease in his late teens and early 20s, which was partly his father's fault for encouraging him to live a wild, promiscuous lifestyle. The Duke took his sons to sample the "pleasures" of Paris and Berlin, something which horrified Albert but appealed a great deal to his older brother.

Ernst's appearance and his health deteriorated, and by the time he visited England in 1839 – on the trip where Albert became engaged – he was noticeably ill, with the Queen's lady-in-waiting Sarah Lyttelton describing him as "very thin and hollow-cheeked and pale".

Still, many wives were considered for Ernst but he remained unmarried until his mid-20s. Prince Albert initially encouraged him to get married, but after he found out about his brother's disease he advised him to wait until he was better.

By 1842 his symptoms had presumably improved because he tied the knot with Princess Alexandrine of Baden. Her parents were only a a minor Grand Duke and the daughter of the deposed King of Sweden, not an ideal match as far as Ernst's ambitious family was concerned – but two years later, Ernst's father died and he himself became Duke.

Alexandrine was an absolutely loyal and devoted wife, but unfortunately the years went by and the marriage remained childless. Even though it's extremely likely that the problem was Ernst's as his venereal disease made her infertile, she blamed herself and stuck by him – while he seems to have shown her little regard. He was unfaithful and continued to have affairs, fathering at least three illegitimate children and at one point bringing two mistresses to live with him and his wife. Alexandrine seems to have turned a blind eye and continued to call him "Ernst, my treasure", baffling outsiders.

After their marriage, Alexandrine and Ernst visited Victoria and Albert in England and the two couples got on extremely well, although the trip had to be cut short when Ernst's new wife became ill. But later, after her husband's death, Queen Victoria expressed her disapproval of both her brother-in-law and sister-in-law: Ernst was embarrassingly open about his lovers, and Alexandrine was scandalously willing to put up with it and be humiliated.

Despite the souring relationship, childless Ernst agreed to take Victoria's second son as his heir to the ducal throne.

Victoria will return for series 3 on ITV