As President Donald Trump and his family trooped into Buckingham Palace for a state banquet with Queen Elizabeth II on Monday night, royal watchers, palace protocol chiefs and journalists were on the alert. Consider, even before Trump landed, he had labeled Meghan Markle “nasty” and the London mayor “a stone cold loser."

For Trump, however, this royal dinner was clearly more than the usual state visit, as the New York Times pointed out on Tuesday. While Trump has worked hard to build his life into a glittering, eponymous brand, there has long been a royal-specific yearning in the Trump family. What is less known is that this desire arguably dates back to Trump’s mother, an immigrant maid who came to America almost 100 years ago and bequeathed to her fourth child the notion that all that glitters really is gold.

While Trump has worked hard to build his life into a glittering, eponymous brand, there has long been a royal-specific yearning in the Trump family.

Unlike his mother's origins, Trump’s obsession with the royals — the human epitome of his old go-to word, “classy” — is hardly a secret. Besides all the gold T’s and his gilded Versailles triplex in Trump Tower, there’s the family crest that Trump essentially stole from the socialite who built Mar-a-Lago, modifying it to remove the word “Integritas” but keeping the three rampant lions.

Indeed, Trump has a long history of seeking royal stardust. In 1981, he made up a story about Prince Charles and Princess Diana planning to shell out $5 million for a Trump Tower condo. In 1994, he claimed that Prince Charles and Princess Diana had sent in $50,000 checks to become charter members of the Florida Mar-a-Lago club, a Trumpian whopper that a palace spokesman sniffed was “complete nonsense.” Trump even tried (and failed) to date post-divorce Diana, who reportedly said he gave her “the creeps.” Prince Charles reportedly declined an invitation to Trump’s 2005 wedding to Melania.

Pundits like historian Doug Brinkley have blamed Trump’s obsession on his autocratic political bent — he wanted to be “King Donald.” Or simply a penchant for outrageous marketing strategies. But the true source is likely a far more personal inheritance: A Trump family secret is that his mother worked as a maid in the household of steel magnate Andrew Carnegie.

Mary Anne McLeod was the 10th child of a fisherman, born into muck boots and peat smoke on a remote Scottish island. She grew up in a two-room cottage and probably got no more than an eighth-grade education before she left the Isle of Lewis in the 1920s, following older sisters who had nestled into a community of nannies, butlers and maids from the British Isles who worked for the robber barons of New York.

Trump has long claimed his mother came to America on a holiday. But the truth can be found in the 1930 U.S. Census, where McLeod is listed at the bottom of a lengthy retinue of butlers, footmen, chauffeurs, cooks and maids working for Louise Carnegie.

It’s not clear how long McLeod held that position, because the Trump family has never acknowledged it. But in 1936, she married Fred Trump, Donald’s father, and moved to Queens. As Fred Trump got richer, Mary Anne modeled herself as a Queens Louise Carnegie — dressing in furs, her blonde hair coiffed into a now-familiar confection, as she was reportedly chauffeured in a Rolls Royce to, some stories say, collect the change from the laundromats at her husband’s growing middle-class apartment building empire.

Mary Anne’s affinity for royal pomp was so deep that she reportedly couldn’t be dragged away from the television set during the coronation of Queen Elizabeth.

Mary Anne’s affinity for royal pomp was so deep that she reportedly couldn’t be dragged away from the television set during the coronation of Queen Elizabeth, even as her thrifty German husband and her even thriftier German mother-in-law scorned her for it.

Donald seems to have inherited that yearning whole — along with his father’s scorn when he moved to Manhattan and put up his glass tower. Trump admits in “The Art of the Deal” that Fred Trump told him that Trump Tower could have been built of cheaper brick for pennies on the dollar.

Late in life, Mary Anne Trump finally did get to spend a small fortune decorating her own mini-palace in one of the Trump Tower condos. But, according to a family member who spoke to me for my book, she never spent a night in it, because her husband, by then enfeebled and suffering from Alzheimer’s, wouldn’t or couldn’t live there.

Donald Trump’s abiding sense of being an outsider is also likely owed to his mother — the girl looking in at the castle window in Scotland, the teen maid peeking down a polished banister into the candle-lit Carnegie dining hall. Donald, born and raised in an outer borough, was rich — but not to the Manhattan manner born.

Trump’s children, however, were born to rich celebrities in Manhattan — and in America, that means they can play at being royal issue. Ivanka writes in her first book, “The Trump Card: Playing to Win in Work and Life,” that her last name is synonymous with class and luxury. Via Instagram, she assiduously curated her family’s arrival in the White House to look like the Camelot of the Kennedys. Meanwhile, her nickname inside the White House was at least initially a pejorative “princess royal,” according to Vanity Fair.

Many American political families would have celebrated the remarkable ancestral story of a royals-struck maid from the British Isles who gave birth to a son who became president of the United States — and who walked into Buckingham Palace Monday to present that woman’s grandchildren to the Queen of England.

But not the Trump clan. For one thing, to admit that they are living out the culmination of that immigrant woman’s dream would be to acknowledge the possibilities that America offers to other men and women.