Previously undiscovered diaries have been found by an author based in the UK which show the intense relationship between Queen Victoria and the Indian man employed to be her teacher.
The diaries have been used by London-based author Shrabani Basu to update her book Victoria and Abdul - which tells the story of the queen's close relationship with a tall and handsome Indian Muslim called Abdul Karim.
The diaries add weight to suggestions that the queen was arguably far closer to Mr Karim than she was to John Brown - the Scottish servant who befriended her after the death of her beloved husband Prince Albert in 1861.
They show that when the young Muslim was contemplating throwing in his job, soon after his employment started, because it was too "menial", the queen successfully begged him not to go.
Mr Karim was just 24 when he arrived in England from Agra to wait at table during Queen Victoria's golden jubilee in 1887 - four years after Mr Brown's death. He was given to her as a "gift from India".
Within a year, the young Muslim was established as a powerful figure in court, becoming the queen's teacher - or munshi - and instructing her in Urdu and Indian affairs.
Mr Karim was to have a profound influence on Queen Victoria's life - like Mr Brown becoming one of her closest confidants - but unlike him, was promoted well beyond servant status.
"In letters to him over the years between his arrival in the UK and her death in 1901, the queen signed letters to him as 'your loving mother' and 'your closest friend'," author Shrabani Basu told the BBC.
"On some occasions, she even signed off her letters with a flurry of kisses - a highly unusual thing to do at that time.
"It was unquestionably a passionate relationship - a relationship which I think operated on many different layers in addition to the mother-and-son ties between a young Indian man and a woman who at the time was over 60 years old."
Ms Basu hints that it is unlikely that the pair were ever lovers - although they did set tongues wagging by spending a quiet night alone in the same highland cottage where earlier she and John Brown used to stay.
"When Prince Albert died, Victoria famously said that he was her husband, close friend, father and mother," Ms Basu said. "I think it's likely that Abdul Karim fulfilled a similar role."
Mr Karim's influence over the queen became so great that she stipulated that he should be accorded the honour of being among the principal mourners at her funeral in Windsor Castle.
"The elderly queen specifically gave this instruction, even though she knew it would provoke intense opposition from her family and household," Ms Basu said.
"If the royal household hated Brown, it absolutely abhorred Abdul Karim."
During his service with the queen, Mr Karim was bestowed with many honours as the royal party travelled around Europe meeting monarchs and prime ministers.
He taught her how to write in Urdu and Hindi, introduced her to curry - which became a daily item on the royal menu - and eventually became her highly decorated secretary.
He and his wife were given residences on all of the main royal estates in the UK and land in India. He was allowed to carry a sword and wear his medals in court - and was permitted to bring family members from India to England.
"Mr Karim's father even got away with being the first person to smoke a hookah [water-pipe] in Windsor Castle, despite the queen's aversion to smoking," Ms Basu said.
"The queen's munshi was named in court circulars, given the best positions at operas and banquets, allowed to play billiards in all the royal palaces and had a private horse carriage and footman."
That Mr Karim inspired the empress of India could be seen not just by her newfound love of curry. Her eagerness to learn Urdu and Hindi because of his teaching was so strong that she even learned to write in both languages - and gave him a signed photo written in Urdu.
She also used his briefings on political developments in India at the turn of the 19th Century to berate successive viceroys, her representatives in India - much to their displeasure - on measures they could have taken to reduce communal tensions.
"At a time when the British empire was at its height, a young Muslim occupied a central position of influence over its sovereign," Ms Basu said.
"It was a relationship that sent shockwaves through the royal court and was arguably a relationship far more scandalous than her much reported friendship with Mr Brown."
Such was the level of ill-feeling he generated that barely a few hours after the queen's funeral, her son Edward VII unceremoniously sacked Abdul Karim.
In addition, he ordered that all records of their relationship - kept at Mr Karim's homes in India and the UK - should be destroyed.
But remarkable detective work by Ms Basu in India and Pakistan unearthed Mr Karim's diaries - kept by surviving family members since his death in 1909 - which detail his 10 years in London between Queen Victoria's golden and diamond jubilees.
The diaries and other correspondence were taken back to India by Mr Karim and his nephew, Abdul Rashid, after their dismissal and were in turn sneaked out of India to Pakistan 40 years later when his family migrated during the violence at the time of partition.
A surviving family member in India read about Ms Basu's book in a local newspaper and told her that the diaries were being kept by another branch of the family in Karachi, which she duly tracked down.
"I was fortunate enough to have unearthed a truly remarkable love story," Ms Basu reflected.
Shrabani Basu's updated book, Victoria and Abdul, is published by the History Press.