Danielle de Niese: The slim lady sings

She's playing Poppea at Glyndebourne – and she's dating the boss. Danielle de Niese has the talent and looks to turn heads, says Jessica Duchen

Danielle de Niese, a petite young woman with a big voice and an even bigger future, has an unusual problem with visa officials. "They look you up and down, and they're like, 'You're an opera singer? You don't look like an opera singer, you look like a pop star.' And I'm like, 'Thank you, but I am an opera singer! The stereotype is changing. This is 2008.'"

Anyone who thinks that a diva is a heavyweight in a winged helmet would be startled when confronted with De Niese, 29. She shot to fame here in 2005, singing Cleopatra in Handel's Giulio Cesare at Glyndebourne in David McVicar's award-winning production: her exotic beauty and star-quality stage presence created shock waves as she was instantly acclaimed as one of the sexiest sopranos ever to set foot on stage. Moreover, there's a charisma that seems to emanate from her voice itself – a notably young but still extraordinarily powerful and bell-like soprano. Her debut CD of Handel arias is just out on Decca, and this summer she's back at Glyndebourne to sing the title role in Monteverdi's L'incoronazione di Poppea.

Watch Danielle de Niese performing Julius Ceaser

But now there's a twist to the Glyndebourne tale: De Niese's name is being linked with that of Gus Christie, the chairman of the Glyndebourne family package. The legend goes that when Gus's grandfather John Christie fell in love with the young soprano Audrey Mildmay, he promised to build her an opera house at the family home in Sussex if she would marry him. She accepted; he kept his word, and Glyndebourne's operatic activities duly began in 1934. The opera house is still very much a family matter; Gus took over after his father George's retirement in 2000. But when Gus broke up in 2004 with his wife of 11 years, Imogen, who took their four young sons with her, the future of Glyndebourne was thought to hang in the balance.

"We are together," De Niese confirms, "and we're having a wonderful time!" She met Gus for the first time at her audition in 2004. "And in 2005 I was working here, but we didn't get together until two years later. It's a surprising but wonderful thing."

Her astonishing looks derive from a background as international as her career. "Both my parents were born in Sri Lanka," she explains, "but they are Sri Lankan Burghers – people of mixed descent from the island's colonial days." Her father had Dutch roots and her mother's family was partly Scottish; they both left Sri Lanka as teenagers and moved to Australia. Danielle was born in Melbourne, where she started classical voice lessons at the age of eight.

When she was 10, the family moved to Los Angeles, not least so that she could study at the Colburn School, which specialises in educating talented children. There she studied more than just classical music – jazz and tap-dancing were also on the agenda. "I was there often at evenings and weekends, and performing a lot – I made my recital debut when I was 12. But at the same time I was very much a normal kid. Though what is normal? I don't know!"

She insists she was never pushed beyond her capabilities and that her parents were supportive. "My dad's in banking, my mum manages the American branch of a Swiss vitamin company; they're really busy, but they still come to all my premieres." She tried her hand at television as a teenager: after she was featured on a programme called LA Kids, she presented the show for several years and won an Emmy. At 18, she became the youngest singer ever accepted on to the Lindemann Young Artists Programme at the Metropolitan Opera, where she made her debut as Barbarina in Le nozze di Figaro. "I wasn't even of a legal age to have a glass of champagne afterwards!"

Her role in Glyndebourne's new production of L'incoronazione di Poppea is, like Cleopatra, that of a powerful, sexy and self-aware woman embroiled with a Roman ruler: Poppea is the mistress of the emperor Nerone. Written in 1642, the work's sophistication and psychological complexity hasn't dimmed with time. The story appears simple: Poppea and Nerone do away with anyone who stands in the way of their love and their power, from their former spouses to the philosopher Seneca. They can come across as ruthless, power-crazed individuals – but when the pair finally marry, Monteverdi presents one of the most beautiful love duets ever composed; we promptly forgive them everything.

With her Covent Garden debut in Handel's Acis and Galatea next season, another Cleopatra at Glyndebourne in 2009 and a dream coming true when she works with her heroine, Dame Kiri Te Kanawa, later this summer, it doesn't look as if De Niese will be off the stage at all for quite some time. As for her off-stage association with Glyndebourne, she wisely refuses to speculate on what the future may hold.

L'incoronazione di Poppea is at Glyndebourne from 18 May (01273 815 000)