Art throbs: Vito Schnabel and Alex Dellal

Move over Jay Jopling and Larry Gagosian, Vito Schnabel and Alex Dellal have arrived.

At first glance the party spilling on to the pavement of Hoxton Square could have been just another of London's nightly exhibition openings. But as one examined the crowd more closely, a series of faces came into focus: Sir Norman Rosenthal, former exhibitions secretary of the Royal Academy; Julia Peyton-Jones, director of the Serpentine Gallery; Alice Dellal, with her tattooed gallery-owner boyfriend Ross Tanner; Tyrone Wood with his girlfriend Rosie Huntington-Whiteley; Gilbert & George; Dasha Zhukova; all present and correct. So how did an unknown gallery showcasing the work of an obscure American surrealist sculptor, Theo A Rosenblum, attract such a glossy turn-out?

The answer lies in the fact that the gallery, 20 Hoxton Square, belongs to Alex Dellal, 25, of the Dellal property dynasty, and the show was curated by Vito Schnabel, 22, son of former taxi driver, celebrated American artist, filmmaker and master bohemian Julian Schnabel. Between them, Alex and Vito have the power to conjure up a sparkling party just about anywhere and frequently do.

I meet Alex, louche, tanned and tousled in flip-flops, jeans and a dark blue T-shirt, two days after the Rosenblum private view, I Didn't Know There Was Chicken in This Soup, with already half the work, priced from £2,000 to £15,000, sold. We convene in his office on the first floor of the cavernous 11,000sq ft building he bought for £2.4 million four years ago for his family property company, Allied Commercial Holdings, to turn into flats: 'But I just fell in love with the space.'

Thanks to the largesse of his property magnate father Guy, the building, with its wooden floors, white walls and floortoceiling windows, is now his gallery, office and home. But 20 Hoxton Square is not the plaything of an idle young plutocrat; Alex's ambitions are philanthropic. While studying photography at the London College of Printing, he fell in with an arty crowd and was struck by how difficult his contemporaries were finding it to put on shows. 'I started helping to put exhibitions together. First it was just in friends' houses, then it started to grow.

'Places like White Cube are intimidating,' continues Alex softly, sipping a glass of water. 'Work is sold in a very elitist way, and for a certain budget. I wanted to do something different. We're not set up like most commercial galleries, booked up six months in advance. We take people in last minute and look at all artists; if you're good, then we'll take you.'

Alex put on his first exhibition at the gallery in September 2006, showcasing a group of youthful unknowns. There have been ten subsequent shows, of which six sold out. A lot of the art, like Rosenblum's, is gloriously amateur (one of Rosenblum's star pieces is a small pig with its head sliced into ham, and sausages for its tail; a symbol of the perils of modern food production), but that's the whole point: to provide a stepping stone for new artists who aren't established or sophisticated - yet.

'We're not competing with the big galleries,' says Alex. 'When White Cube and Gagosian start stealing our artists we'll know we're succeeding. And in ten years' time, it's my dream that all the big artists of the age will have passed through 20 Hoxton Square.'

In addition to scouting graduate shows for talent, Dellal edits a free bimonthly in-house paper, 20 Hoxton Square, written by artists for artists, as well as speculating, buying and developing property for his father's company.

The Dellal name has always been synonymous with risk-taking and riches. Alex's grandfather, 'Black' Jack Dellal, so called because of his success at the gaming table, is a multimillionaire property tycoon whose wealth is estimated at around the £500 million mark. Alex's punky little sister, Alice, 21, is a face of Mango, the body of Agent Provocateur and is known for her half-shaven head; while his other sister, Charlotte, 28, is a shoe designer whose creations have been worn by Sienna Miller and Kate Moss. Alex's girlfriend is equestrian, journalist and European royal Charlotte Casiraghi, the dewy daughter of Princess Caroline of Monaco. The photographer Mario Testino is his godfather and Elizabeth Jagger is an ex (they split in April 2004 after a six-month relationship).

It was a glamorous life from the outset. Alex was born in Cape Town, where his father Guy was studying, and grew up in the UK and Rio, hometown of his mother, former Yves Saint Laurent model Andrea de Magalhaes Viera. His parents married in 1982, divorced in the mid-1990s and then remarried in 2001. Friends of the family say their relationship was always tempestuous and were not surprised when they split, nor when they remarried. 'It was the best thing that could have happened,' Alex says. 'We're such a close family; it's great they're now back together.' Neither party remarried in the interim, which must have made the situation easier, although even without the divorce, it must have been unsettling to be perpetually on the move. As a result of the constant upheaval, Alex went to a total of 13 schools, including a two-and-a-half-year stint at Bedales, where his sisters were educated.

Alex also has a little brother Max, 18, and the family 'spend almost every weekend together' at their Hampshire estate, Manor Farm in Brown Candover, near Basingstoke, which was a refuge in the 1990s for the late Michael Jackson, a family friend, when he was trying to recover from his addiction to prescription drugs. Their other family home is on Pelham Crescent, Knightsbridge, the perfect base for the partying clan.