The royal family might seem like the epitome of propriety with their fancy titles and official names, but behind closed doors, they like to lean into more informal labels. Prince William and Kate Middleton reportedly had Prince George’s nickname selected even before he was born (and before he was dubbed “PG Tips” by his classmates), and Prince Harry’s moniker is actually a nickname for his actual name, Prince Henry. King Charles has also extended the practice by coming up with his own terms of endearment for his two daughter-in-laws–and the British monarch’s nickname for Meghan Markle is so unexpected.

The Suits alum already uses a nickname by going by her middle name, as “Rachel” is actually her first name. However, King Charles came up with his own informal title for Markle while she was still a working royal–and it shows how much he respected her “tough” and “unbending” nature, according to royal experts. The then-prince dubbed Markle “tungsten,” referring to the hard and brittle metal that has the highest melting point of any known element, as a compliment.

“Prince Charles admires Meghan for her strength and the backbone she gives Harry, who needs a tungsten-type figure in his life as he can be a bit of a softy,” a palace insider previously told the Mail on Sunday. “It’s become a term of endearment.”

Royal correspondent Katie Nicholls also previously spoke on Charles’s nickname for Meghan while revealing how the pair became close before her 2018 wedding to Prince Harry. In her 2022 book The New Royals: Queen Elizabeth’s Legacy and the Future of the Crown, the royal expert revealed that Markle’s “resilience” came through during her first official royal engagement: A joint appearance with Prince Harry and Prince William and Kate Middleton at the Royal Foundation Forum.

“It was, according to one aide, the moment William and Kate, who was heavily pregnant, realized they needed to up their game,” Nicholls wrote at the time. “The Cambridges had already signaled their intention to be more than ‘ornamental royals’ and had, along with Harry, made a huge success of their mental health campaign ‘Heads Together.’”

However, Charles noticed that Meghan was “the breakout star of the foursome,” a palace insider told Nicholls. “She was polished, passionate, and funny, using all her TV-honed skills to present her case. That was a wake-up moment for William and Kate when they realized that Meghan was very impressive, very confident, and very capable, according to a source.”

While Prince Harry and Meghan Markle are estranged from King Charles and the rest of the royal family amid their ongoing feud, the monarch has only gotten closer to his other daughter-in-law Kate Middleton amid their cancer battles last year.

Royal author Robert Jobson revealed that Middleton and Charles reportedly have sweet nicknames for each other in his book Catherine, the Princess of Wales. Apparently, the Princess of Wales calls Charles “Grandpa,” while the king likes to address Kate as his “beloved daughter-in-law” or “darling daughter-in-law.”

In addition to their “close connection” and easy camaraderie, demonstrated by how they’re often spotted “laughing and joking together,” Kate’s personality as an “instinctive peace-maker” has smoothed the way for William and his father to have a better relationship than they had in the past.”