Abigail Kinoiki Kekaulike Kawānanakoa, Hawaii's so-called "last princess", has passed away aged 96.
The royal, known to her friends as Kekau, was one of the last living links to the royal family and was celebrated for her philanthropic support of traditional Hawaiian culture.
The heiress died peacefully at home in Honolulu on Sunday with her wife by her side, according to a statement released by Iolani Palace, the historic home of the royal family - and America's only royal residence.
"Abigail will be remembered for her love of Hawaii and its people," said her wife, Veronica Gail Kawānanakoa. "I will miss her with all of my heart."
No cause of death has yet been given.
Abigail Kawānanakoa was born in Honolulu in 1926 and later attended school in Shanghai and California.
Her great wealth, which is estimated to be $215m (£175m) and was held in trust, came from her great-grandfather, James Campbell, an Irish businessman who owned a sugar plantation.
His daughter married Prince David Kawānanakoa, who was third in line for the throne of the Kingdom of Hawaii when the royal family was overthrown by American businessmen in 1893.
At the time, the role of US nationals in the coup was controversial, and President Grover Cleveland describing their involvement in the overthrow of the Hawaiian monarchy an "embarrassment".
After the prince's death in 1908, his widow adopted their grandchild through the traditional Hawaiian custom of "hānai", which strengthened Abigail's claim to the informal title of princess.
While some genealogists claimed that Princess Kawānanakoa had the strongest royal ties to Hawaii, a separate offshoot of the former royal family claims that Princess Owana Ka'ohelelani is the rightful head of the modern-day dynasty.
Mrs Kawānanakoa herself admitted in a 2021 interview with Honolulu Magazine that had the monarchy survived, her cousin Edward Kawānanakoa would have been in line to rule ahead of her, based on the rules of succession.
"Of course I would be the power behind the throne, there's no question about that," she joked in the interview.
Among her acts of philanthropy, Mrs Kawānanakoa funded scholarships for indigenous Hawaiians and contributed to the upkeep of Iolani Palace, which is now a museum.
The Abigail KK Kawananakoa Foundation, which was set up in 2001, put aside $100m (£81m) of her wealth to support native Hawaiian causes upon her death, according to the Honolulu Star-Advertiser.
Friends also praised her sense of mischief, and she was known to test religious leaders for offering them large sums of money - sometimes in exchange for outrageous demands.
Jim Wright, who was her personal lawyer from 1998, recalled that she once agreed to a request from the Catholic Diocese of Honolulu of $100,000 (£81,281).
She agreed to make the payment - but only if she could get a photo of Pope Benedict XVI accepting her cheque.
Hawaii's governor, Josh Green, was among those to pay tribute to Mrs Kawānanakoa, saying he and his wife were "deeply saddened" by the loss.
"Abigail bore the weight of her position with dignity and humility, enriched the lives of everyone she touched, and like so many Aliʻi who came before her, she has left a legacy dedicated to her people in perpetuity."
He had ordered that flags be flown at half mast for the rest of Sunday in her honour.
However, Hawaiian activist Walter Ritte has told local media that her impact on indigenous culture was minimal.
"We didn't quite understand what her role was and how she could help us," he is quoted as saying.
But Senator Jarrett Keohokalole and Representative Daniel Holt, leaders of the Native Hawaiian caucus in the state legislature, hailed her generosity and contributions, which they said had greatly aided the island's culture and community.
In a court appearance in 2019 over the management of her wealth, she told the judge that "heritage dictates that I must take care of the Hawaiian people".