It may have begun, as many things have, with Madonna.

For her 2000 wedding to Guy Ritchie, the singer donned an antique diamond tiara, and later donated it to charity. But model Stella Tenant also deserves credit for turning the tiara on its head. In a 2003 advertising campaign for French jeweler Chaumet, she wore one pushed back like a hairband, exuding an air of casual, decadent luxury.

Tiaras used to be the accessory of choice only for royal weddings, beauty pageants, and playing dress-up. The pieces were so passé that dealers would pry them apart in order to resell the individual gems, says Stephen Forward of Beverley R, a period-jewelry specialist at Grays Antiques market in London.

But over the past few years, the demand for tiaras and hair jewels has been growing.

Last September, actress Keira Knightley wore a Bulgari Vintage Collection diamond necklace as a tiara at the London premiere of Atonement. Scarlett Johansson, as Cinderella in a new Annie Leibovitz-photographed Disney ad, wears a 62-carat, $325,000 Harry Winston diamond tiara.

In June 2007, a diamond tiara made circa 1890 fetched a world-record auction price of more than $2 million at Christie’s London. It helped that the piece was made by Fabergé and hailed from the collection of Maria Gabriella di Savoia, an Italian princess. But the final price was still far above the $1.2 million high estimate. A year earlier, the Poltimore tiara, worn by Britain’s late Princess Margaret at her wedding, sold for $1.7 million to a Chinese collector.

“Recent interest in antique tiaras is partly due to the public realizing [they] are becoming scarcer,” says Raymond Sancroft Baker, jewelry director for Christie’s Europe. He has seen many a parent buy a tiara in anticipation of a daughter’s wedding—with the daughters being as young as five.