King Charles has a code name for Meghan Markle - and if could offer some clues towards the Royal Family's true feelings for the Duchess of Sussex.
The monarch settled on calling his son Prince Harry's wife "Tungsten" five years ago - and it's understood to be quite the compliment.
It is claimed he gave his daughter-in-law the moniker when the pair got engaged back in 2017.
The meaning of the nickname for the former actress gives a glimpse at his opinion about her, one expert suggests.
Tungsten, in this context, is often used to describe someone who demonstrates toughness and a resilient nature.
According to Christine-Marie Liwag Dixon, Charles uses the code name in a flattering way.
Speaking to viewers of The List, she explained: "Meghan Markle hasn't had an easy time of it since joining the Royal Family.
"She has also said that she felt less than at home in the Royal Family.
"The Royal Family may not have approved of Meghan and Harry stepping down as senior royals despite them doing so to escape an environment that was clearly not good for their mental health.
"However it seems that Prince Charles had a lot of respect for Meghan's resilient nature."
Christine-Marie went on to explain what the nickname means as she continued: "This was evident in the secret nickname he reportedly had for her.
"Charles nicknamed her after the metal as 'she is tough and unbending'. Tungsten is the strongest naturally occurring metal on the planet."
Within the walls of the palaces, the Royal Family have nicknames for each other - and some of them are very lighthearted.
Kate is reported to jokingly call her husband Prince William 'Baldy', while William responds by sometimes referring to her as the Duchess of Dolittle.
Earlier this week it was claimed Prince Harry and Meghan were engaged in secret for months before their big public announcement.
The Duke and Duchess of Sussex told the world they were engaged in late November 2017.
The beaming pair posed for the cameras in the chilly garden at Kensington Palace, with a royal statement saying Harry popped the question 'earlier this month'.
But it has now been claimed the couple got engaged around four months before and that Meghan had already said yes when she went on the cover of Vanity Fair to confirm they were dating.
It means the pair would have been dating for less than a year when Harry asked the actress to be his wife.
But a new book has claimed they were 'privately engaged' months before their public announcement, but didn't want anyone to know.
Valentine Low's Courtiers: The Hidden Power Behind The Crown, discussed Meghan's interview with Vanity Fair in October that year.
"The interview was, in effect, Meghan’s big launch," she wrote.
"The couple were not officially engaged — though everyone in Kensington Palace knew they had been privately engaged since the late summer — but this was Meghan putting herself out there in a confident, pro-active way."
