The teenager was found unresponsive in the family's Florida mansion on Saturday afternoon.
David and Jackie Siegel, the subjects of the 2012 documentary The Queen of Versailles and owners of Westgate resorts, are mourning the loss of their daughter Victoria Siegel.
The 18-year-old was found unresponsive in the family's Windemere, Florida, home just after 2 p.m. on Saturday afternoon, the Orlando Sentinel reports.
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Victoria was taken from the mansion on Green island Cove to the Health Central Hospital, where she was pronounced dead. Orange County Sheriff's Office spokesperson Jef Williamson said investigators are still ruling on the cause of death.
"It is a sad case," Williamson told People magazine.
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Jackie confirmed her daughter's death in a Facebook post on Sunday. "It is with great sadness that we ask you to respect our privacy during this tragic time and the loss of our beloved daughter, Victoria," she wrote. "Thank you all for your prayer and for your support."
She added that the family is not commenting on the death of Victoria, the second oldest of the Siegel's eight children, at this time, but the family will share more information as they receive it.
The family was most recently in the public eye just last week when David and Jackie appeared on ABC's Wife Swap.