Updated May 19, 1997 12:00 PM

In the world of fairy-tale memorabilia, the only more coveted item may be Cinderella’s slipper: On June 25, glamor will be up for grabs—big time—when 79 of the cocktail dresses and ball gowns from the Kensington Palace closets of Diana, Princess of Wales, will be auctioned for charity at Christie’s in Manhattan. “It’s unique,” says Meredith Etherington-Smith, Christie’s London-based creative director, “because it’s a royal collection. They have given dresses to friends before but never actually sold them.” In our Contents section and on the following pages, PEOPLE presents an exclusive preview of 60 elegant dresses on the block.

Just 10 of the designs were unveiled last February, when the sale was announced. Now, six weeks before the divestiture, the catalog for the auction (the dresses are numbered Lots 1 to 80, with Lot 13 omitted, a bow by Christie’s to superstition) is still under wraps. The $60 paperbacks (inset, above), $265 hardcovers and $2,000 limited editions (250 copies) in violet leather won’t be available until May 17, but Christie’s has fielded orders for 3,250 copies. One eager customer tried to prepurchase every copy of the limited edition (Christie’s declined).

Reflecting the work of London designers including Catherine Walker, a French-born couturiere, as well as Victor Edeistein and Bruce Oldfield, the collection provides a telling glimpse of Diana’s 15 years as a royal and her transition from ingenue to confident single woman. Some dresses have never been seen in public; others helped fuel her reputation as one of the world’s most glamorous women. All, it seems, are now regarded by the princess—determined to make her mark as a philanthropist—as part of her past.

“In the ’80s, Diana epitomized romance,” says Elizabeth Emanuel, 43, who, with then-husband David, created the earliest gown in the preview—a blue tulle worn to a performance of the Welsh National Opera in 1982, when Di was a guileless 21. Among the most recent dresses is a navy silk sheath by Walker chosen for a Manhattan awards gala staged by the Council of Fashion Designers of America in January 1995, seven months after Charles’s admission of adultery. With her hair slicked into a ducktail, Di looked chic and toned—prompting presenter Fran Drescher to joke, “She is the best dressed princess I know—besides me.”

Not that all of Di’s dresses were hits. Evening gowns designed for her when she was a newlywed featured “the meringue effect of the tight bodice and huge skirt,” as Hilary Alexander, fashion editor for London’s Daily and Sunday Telegraph, puts it. “Before she was engaged, fashion didn’t really encroach on her life. She overcompensated [with] frills, ribbons, bows and lace.”

Influenced by the glitz of the mid-’80s, Di traded the bows for sequins during her “Dynasty Di” phase. That was followed by the high-glam look: Single-sleeved gowns and column dresses with boleros became her signature. They weren’t to everyone’s liking: Of one high-collared, beaded design Walker created in 1989, Paula Reed, fashion director of London’s Harpers and Queen magazine, says, “It would be impossible to have a conversation with someone next to you unless you wanted to look like someone peeping over a garden hedge.”

The Waleses’ 1992 separation and Di’s brief retirement from public life gave her a final push away from showy designs. “That was a milestone that would make anyone reflect on who they are and how they look,” says Reed. “Everything in her wardrobe became more low-key.”

Honor-bound to use British talent, Di tested her wings with designers including Zandra Rhodes, 56, and Oldfield. “Things had to be quite showy,” Oldfield, 46, says of dressing a royal. “Every day she was the mother of the bar mitzvah boy. She’s got very good legs, so you could show a lot of leg. But [you’d often] take a dress which was quite sexy and [have to] modify it.”

Like other dresses in the sale, the five by Oldfield came either from his collection—which, from 1980-90, when Di was a client, ranged in price from $1,800 to $15,000—or were designed for special occasions. “She was very involved,” he reports. During fittings at Kensington Palace, “you’d have to be fast because she didn’t have much patience.”

Though publicity-shy, Walker, who has 50 gowns in the sale and is one of the few auction designers who still work with Di, admits that they are close. Battling breast cancer since 1995, Walker says that Diana has offered “unfailing support” during her illness and that she is “deeply moved that my designs…are now being used to save lives.”

Each season, Diana visits Walker’s atelier. About half her orders come from the collection (which starts at about $6,000); the rest are custom-designed. Though Diana makes suggestions, it is the designer’s vision that prevails, says Walker, 50. “My clients choose me,” she says, “when they want my handwriting.”

And discretion. Like other designers, Walker keeps careful records of which client orders a particular gown and of where she plans to wear it. Edelstein, too, made a point of heading off conflicts. “The understanding,” says the 51-year-old designer, who worked with Di until 1993 before retiring to Spain, “was that if she chose something from the collection, one wouldn’t make it for someone else in the royal family.”

There were other constraints, says David Sassoon, 62 (who designed two of the dresses in the auction and whose gowns begin at $3,000). “For state visits,” he says, “royals have to wear medals and sashes, the kiss of death for any dress.” Creasing is a concern too, he adds. “And we always put in extra linings, since they have to avoid anything see-through.”

Rules aside, designers say Diana, 35, is a model customer who always paid in full. “She was probably the most agreeable we had,” says Edelstein, whose dresses fetched up to $8,000. “It’s always a collaboration—you each make suggestions and ask, ‘What do you think?’ ”

The question now is what Diana’s size 8-10 wardrobe will bring on the block. Fueled, perhaps, by the success of high-end auctions like the sales of the Duchess of Windsor’s jewels and Jacqueline Onassis’s mementos, the event is expected to net $2 million to $4 million. Still, says Bruce Wolmer, editor-in-chief of Art & Auction magazine, “it’s pure desire, and when pure desire gets going, it’s very hard to predict.”

According to Taggarty Patrick, a Christie’s vice president, bidding will begin at $5,000. But since there is no reserve (i.e., minimum bid), she says, “every dress will be sold.” In the U. S., proceeds will go to the Evelyn H. Lauder Breast Center of Memorial Sloan-Kettering Cancer Center in Manhattan, the AIDS Care Center of the New York Hospital-Cornell Medical Center and Harvard AIDS Institute.

As to who’ll be queuing up, Patricia Hambrecht, managing director of Christie’s for North and South America, says that orders for catalogs (either via the mail or calls to 1-800-395-6300) have come from “a variety of sources—private collectors, costume institutes and museums, people hoping to donate to museums.” Most are Americans: “For the British elite, it would be questionable to be seen bidding on this stuff,” says Wolmer. “Because Di’s reputation has more of a social gloss [in America], you’re more likely to see high bidding in New York.”

On June 25th, 1,100 bidders will be allowed into the auction; all must be catalog holders, and admission will be determined by lottery. Some designers, at least, are at a loss to explain what buyers will do with their booty. “I hope that museums will buy [the dresses], because that’s where they should be,” declares Edelstein. “I can’t imagine anybody wearing them.”

“Unless it fits or you’re a particularly ambitious drag queen…what do you do?” wonders Wolmer. “The punch line is probably the emotional reward. You can tell yourself, ‘I really want it, and besides, it’s for a good cause.’ ”