Huguette Clark, the 104-year-old copper heiress whose intensely reclusive lifestyle and collection of empty mansions has made her the subject of public curiosity in recent years, died this morning at Beth Israel Medical Center, where she had been registered under a pseudonym, according to MSNBC.

Clark is best known in New York City real estate circles as the owner of a 42-room spread at 907 Fifth Avenue valued at around $100 million, though she hadn’t been seen there since she was hospitalized 20 years ago. Martha Stewart reportedly had her sights set on the place.

Throughout most of the past two decades, Clark was in fine physical health and had access to a reported fortune of $500 million-plus but opted instead for a sparse, guarded room at the hospital to which few were granted access — one of her former attorneys talked to her through a closed door after over 20 years of representing her, never meeting her face to face.

In addition to her Manhattan apartment, the largest known apartment on Fifth Avenue, Clark had a 52-acre estate in New Canaan, Conn. that’s on the market for $23 million, which she never lived in, and an oceanfront estate in Santa Barbara, Calif., also worth roughly $100 million, which she hadn’t visited since the 1950s. All of the homes are said to have been meticulously kept up, with full-time caretakers.

Clark’s estate is also the subject of a criminal investigation centering on how her attorney and accountant handled her finances. Neither the accountant nor the attorney has been accused of a crime, though the investigation continues, and it is being prosecuted by the same team that handled the Brooke Astor case. Clark’s estate is worth an estimated four times that of Brooke Astor.

Last year, it was reported that a Manhattan district attorney, who met with Clark at the hospital multiple times before her death, had discovered that the heiress had no living will. [MSNBC]