The Greek billionaire Athina Roussel Onassis married a Brazilian Olympic equestrian Saturday night in a palm-tree lined estate, celebrating with more than 1,000 bottles of champagne.

On grounds surrounded by trees and azalea bushes, the 20-year-old granddaughter and heiress of the late shipping tycoon Aristotle Onassis wed Alvaro Afonso de Miranda, a 32-year-old divorced father and son of an insurance company owner.

The nuptials were shrouded in secrecy, with 400 private security guards warding off paparazzi from all over the world. Guests had to park outside the grounds and pass through metal detectors.

Luxury vehicles whisked them to the ceremony at the Maria Luiza and Oscar Americano Foundation, an 18.5-acre property with a museum, tea house and cultural center. The estate is in Sao Paulo's upscale Morumbi district, near the governor's palace.

Mario de Oliveira, a worker at the estate, confirmed only that the couple got married.

The grounds had been sealed off for a week, with green plastic covering a surrounding chain-link fence to keep passers-by from peering in.

Still, plenty of details emerged ahead of the wedding.

The bride was expected to wear Valentino, and more than 1,000 bottles of Veuve Clicquot champagne were to be opened, the groom's father, Ricardo Miranda, told Brazil's IstoE Dinheiro magazine last week.

The ceremony was ecumenical because Onassis is Greek Orthodox and the groom is a divorced Roman Catholic. Brazil's Veja magazine reported that the couple signed a prenuptial agreement protecting all assets acquired before marriage.

Instead of gifts, the couple asked that guests make donations to Sao Paulo's Aconchego day care center for underprivileged children, IstoE Dinheiro reported.

Miranda, popularly known as Doda, was a member of the Brazilian showjumping team that won bronze medals in the 1996 and 2000 Olympics.

The couple, who share a love for horses and showjumping, met in 2002 at a riding center in Belgium.

A year later, Onassis moved to Sao Paulo, where she shares a 10,650-square-foot apartment with Miranda and Viviane, his 6-year-old daughter from a previous marriage, IstoE said.

Onassis, one of the world's richest women, was raised in Switzerland by her French-born father, Thierry Roussel, and inherited an estimated $2.7 billion from her grandfather on her 18th birthday.

Aristotle Onassis, who married Jacqueline Kennedy Onassis in 1968, died in 1975. The bride's mother, Christina Onassis, died of a heart attack in 1988.