Her own background should have helped prepare her for the formidable challenge.
The Middleton clan is blessed with strong ties and commercial savvy. Kate's parents, Michael and Carole, went from airline employees to owners of a successful small business who gained their children access to Britain's loftiest social circles.
Michael Middleton was a flight dispatcher and Carole Goldsmith a flight attendant before they married and, in the 1980s, set up Party Pieces, a business selling balloons, candles, streamers and other mail-order party supplies.
They did well enough to move from a semidetached suburban house to a large home in the affluent village of Bucklebury, with children Kate, now 29, Pippa - now 27 and her sister's maid of honor - and James, 24. Neighbors speak well of them and guard the family's privacy. Resident Brian Ward remembered Middleton as "a very ordinary girl" who would often pop into the local pub.
The Middletons strive to give their children every advantage in life. The siblings attended Marlborough College, a 30,000 pound ($47,000) a year boarding school attended by some of Britain's wealthiest people. Its alumni include /*Prince William*/'s cousin, Princess Eugenie.
Kate went on to the 600-year-old St. Andrews University in Scotland, where her fellow students included - fatefully - */Prince William*/, the second in line to the throne.
The family also owns a million-dollar apartment in London's tony Chelsea area, where the children have lived while working in the capital.
All have also worked for the family firm.
Affluent as the Middletons are, they are ordinary and middle-class enough to seem to many like a welcome breath of non-aristocratic fresh air for the royal family.
"I think Kate's family journey mirrors that of millions of British people, who have gentrified over the last century," said Claudia Joseph, author of "Kate: The Making of a Princess."
Kate's ancestors on her mother's side were manual laborers and coal miners, a fact trumpeted in tabloid headlines like "From pit to palace." The family runs a small business, like many other Britons.
Kate even has an embarrassing wayward uncle, Gary Goldsmith, who lives in a house in Spain called "La Maison de Bang Bang" and was filmed in 2009 by an undercover reporter apparently taking cocaine and bragging about his royal connections.
However, Kate's paternal ancestors, the Middletons, have been affluently middle-class for more than a century: merchants, lawyers and mill owners in the northern English county of Yorkshire who amassed comfortable fortunes, sent their children to private schools and became pillars of the community. Their money helped Michael and Carole Middleton give their children a leg-up.
In the stratified world of the British upper crust, Middleton's mercantile origins still elicit some snobbery. There were snide comments after Carole Middleton was snapped chewing nicotine gum at William's military college graduation ceremony, which was attended by Queen Elizabeth II. There's the oft-repeated anecdote about William's posh friends quipping "doors to manual" as a gibe at her former airline job.
The family has kept a dignified silence, not speaking to the press apart from a brief statement expressing delight at Kate's engagement and welcoming William to the family.
"I think the snobbery comes from a few stuffy courtiers who are disgruntled that William has married a 'commoner,"' Joseph said in an email interview. "But I think the royal family is delighted that William is marrying the woman he loves. You can tell by the reaction of Harry, who welcomed Kate into the family like a sister, that she has won the Windsors over."