WASHINGTON - Rachel "Bunny" Mellon, the aristocratic philanthropist and a close friend of Jacqueline Kennedy who provided money used to conceal 2008 U.S. presidential candidate John Edwards' extramarital affair, has died at the age of 103, her attorney's office confirmed on Tuesday.

Mellon, an avid, self-taught horticulturist who redesigned the White House Rose Garden during the Kennedy administration, died on Monday at her Virginia estate of natural causes related to her age, according to a statement from Alex Forger, Mellon's personal attorney.

Mellon came from a wealthy background and married into the Mellon banking family. She had a fortune estimated by Newsweek magazine at US$400 million (S$505 million) in 2011, even as she and her husband, Paul Mellon, gave away millions during their lives.

Mellon was the toast of high society. She entertained Britain's Queen Elizabeth and Prince Philip at Oak Spring in 1957 and years later played host to Prince Charles and Princess Diana.

She was a close friend of first lady Jacqueline Kennedy, serving as a mentor in the matters of decorating, art and antiques during John F. Kennedy's presidency. She used her gardening expertise in the White House Rose Garden in the 1960s.

Before becoming a figure in the Edwards scandal, Mellon had lived quietly, spending much of her time at Oak Spring Farms, her 809 ha home in Virginia, about 80km west of Washington, DC.

Newsweek said the estate, with a staff of 120, featured an airstrip, a pool house designed by I.M. Pei and a separate library for her 10,000 horticulture books.

Mellon was introduced to Edwards, the married former North Carolina senator, in 2006 by a mutual acquaintance and came to like his "very deep intelligence," she told Newsweek in a 2011 interview. She eventually contributed more than $3.5 million to organizations and political action committees supporting Edwards.

According to Edwards' aide Andrew Young, Mellon told the candidate she would do "whatever it takes to make you president." Mellon had always shunned publicity, but her support for Edwards made her a key figure when he went on trial in 2012, accused of using campaign money to take care of his mistress, Rielle Hunter, when she was carrying his child. Some $725,000 of that money came from Mellon.

Young, who at first falsely claimed responsibility for the pregnancy to shield his boss, wrote in a memoir that Mellon would send checks hidden in boxes of chocolate - checks that were known in the Edwards camp as "Bunny money." The defense claimed her money was sent as a gift, not a campaign donation.

Because of her age, failing eyesight and health, Mellon did not testify at Edwards' trial and her lawyer said Mellon had no idea her money was going to Hunter. Edwards was acquitted on one count of accepting illegal contributions and jurors deadlocked on five related charges.

Mellon seemed to bear no ill will toward Edwards.

"He would have been a great president," she told Newsweek."He and I were great friends. Every time he'd go on a debate against Hillary (Clinton), he'd call and we'd talk ... I was so surprised when this thing came up." Mellon was also a peripheral player in another criminal case. Her investment adviser, Ken Starr, was sentenced to 7-1/2 years in prison for a 2010 Ponzi scheme that stole $33 million, including $5.57 million from Mellon.

Mellon grew up in wealth as Rachel Lambert in Princeton, New Jersey. Her grandfather had developed Listerine mouthwash and her father, who became part of the Warner-Lambert manufacturing company, made the brand successful as a cure for bad breath.

In 1932, she married Stacy Lloyd Jr, who worked in London for the U.S. Office of Strategic Services, a forerunner of the Central Intelligence Agency, with Paul Mellon.

After the war, she and Lloyd divorced and in 1948 she married Mellon, whose first wife had died of an asthma attack two years earlier. Newsweek said Paul Mellon died in 1999 at 91.

The Mellons were avid art collectors who owned hundreds of works by artists such as Cezanne, Monet, Degas and Rothko, many of which they donated to the National Gallery of Art.

Newsweek said Mellon planned to leave some of her fortune to family members, but that the bulk would go to a foundation to finance a library and school for arborists.

Mellon's wealth was such that she had the Givenchy design house make all her clothing, even her underwear, tennis hats and her servants' uniforms. At one time, she had homes in New York, Washington, Paris, Antigua as well as in Cape Cod and Nantucket in Massachusetts.

Mellon had two children from her first marriage and two stepchildren from her marriage to Mellon.