Athina Roussel Onassis, the sole heiress to the billion-dollar fortune of late Greek shipping tycoon Aristotle Onassis, on Saturday married a Brazilian equestrian champion in an extravagant wedding in Sao Paolo amid draconian security.

Onassis, 20, was married to 32-year-old Alvaro Affonso de Miranda during a lavish ceremony which brought together more than 700 guests but was closed to the press.

Athina met the Olympic medallist and top industrialist, who has a six-year-old daughter from a previous relationship, in 2002 when she began horse riding classes. The couple reportedly moved into a 1,000-square-meter Sao Paolo penthouse a few months ago.

The bride’s father, Thierry Roussel, who has challenged Athina for control of her fortune and has questioned Miranda’s motives for marrying her, was not present, local reporters said. Athina’s mother, Christina Onassis, died at 37 in 1988 following a drug overdose, alleged to have been self-inflicted.