Rebecca Sieff fell in love with Castle Howard when she was 14 years old. Every week she was glued to her TV set watching Brideshead Revisited, ITV's epic drama series, filmed at one of England's largest private stately homes. She remembers,"It looked so glamorous and so wonderful, and you thought, I'm not going to end up in a shitty little house anywhere.… I want to live there." The obsession remained. When Rebecca was 20 and a budding socialite, a magazine interviewer asked her where she would like to live. She responded, "Oh, somewhere like Castle Howard." Now, 14 years later, she does.

Rebecca became mistress of the Yorkshire palace last June when she married its owner, the Honorable Simon Howard. The bride wore a Cartier tiara, the pride of the Howard-family jewels, and a couture crystal-trimmed bridal gown that one of the 250 guests thought "looked more Las Vegas than North Yorkshire." Rebecca never found out how much it cost, since it was paid for by her father. As the new Mrs. Howard moved through the crowd, she was trailed by an army of red-coated footmen and trumpeters, who played a fanfare every few minutes. The spectacle set the tone for Rebecca's style. Driving her black Mercedes convertible through quiet, understated Yorkshire, she sticks out like the Hope Diamond in a yoga class. The novelist Piers Paul Read, a former neighbor of Simon Howard's, explains:"Yorkshire has that usual English thing of you shouldn't be seen to try too hard. They might decide Rebecca is vulgar, really. It's like if Barbra Streisand suddenly hit your local village."

Rebecca says she is still getting used to her neighbors' ways. "It's perfectly awful, but the thing I found out when Imoved to Yorkshire is nobody can live somewhere normal. It has to be 'House,' 'Park,' 'Grange.' You can't just have a house with a number."

She adds,"I cannot go into the village [of Malton] without most of them looking at me like I've descended from Mars."

Rebecca is a member of the Sieff family, who founded the British retailer Marks & Spencer—famous for selling capacious underwear and men's sweaters. Growing up between Belgravia and Hampshire, she was groomed in the old-fashioned way for a life of privilege. She got a conventional education at Millfield, one of Britain's most expensive private schools, and learned to ride competitively. She took piano lessons and played Mozart and Beethoven to concert standard. She spent weekends at her grandparents' house reading history books and improving her knowledge of art and culture. But, thanks to rashly picking up her friends' tabs and what she calls "living," she burned through her "small" trust fund by the age of 27. This left her, socially, in no-man's-land. She was part of neither the county set nor the nouveau riche. As one London socialite puts it, "She's not posh. She's not an aristocrat."

Rebecca has long dark hair and glittering blue eyes. An American size 8, she is unfashionably voluptuous. "Someone said to me, 'Iam mesmerized by your eyebrows,' and I said, 'So am I—they're the thinnest thing I possess.'" In a country where aristocratic wives reserve passion for the four-poster, she oozes sex, right down to her scarlet fingertips. "I don't paint my nails every day, but I never don't have painted nails. Ever, ever, ever."

On the day we meet, she says, while puffing on a Marlboro Light, that she is three months pregnant with twins. She is wearing high heels by Christian Louboutin and a bright-yellow strappy sundress that ends mid-thigh. The most startling thing about her appearance is the jewelry. She has tea-bag-size pink Art Deco earrings. The diamond on her engagement ring hangs over the width of her finger. Her makeup is flawless.