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Heiress' art collection worth millions up for grabs

It's not every day that an iconic painting from one of the world's greatest painters hits the auction block. It's also an extremely rare moment when it's the first time it's been seen in almost a century.

On May 6, Christie's will auction a water lily painting by Claude Monet from the estate of Huguette Clark that has not been exhibited since 1926.

Not only is this 1907 Monet masterpiece important, but its mysterious provenance could add big to the final price tag, according to Brooke Lampley, head of impressionist and modern art at Christie's.

"It's a sensation, it's more than the market can even ask for. This is a perfect storm," Lampley said.

Although many people will not recognize Clark's name, her family was American royalty during the Gilded Age—a time when mining, banking and railroad titans were some of the richest and most powerful men in the country.

Clark was the daughter of William Andrews Clark, the so-called Copper King, who struck it rich in the Montana copper mines.

"It's a great American story," Lampley said.

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The family patriarch left behind a fortune worth more than $300 million to his daughter Huguette, who later became known as the "reclusive heiress." She went into seclusion in the early 1960s, remaining hidden for the rest of her life.

She passed away in 2011 at the age of 104 and Christie's auction house is selling more than 400 items from her estate. Some of the items include paintings by legendary artists Monet and Pierre-Auguste Renoir, rare books, jewelry and even a Stradivarius violin.

(Image: This 1907 Claude Monet "Nympheas" painting from Huguette Clark's collection, pictured above, is estimated to sell for $25 million to $35 million at Christie's on May 6, 2014. Source: Christie's Images Ltd. 2014)

Lampley told CNBC that Monet's "Nympheas" masterpiece was hanging in a sitting room in one of Clark's three sprawling apartments on Fifth Avenue in New York City.

"She enjoyed her privacy and an incredible selection of artworks that she surrounded herself with," Lampley said.

"It's being offered at an estimate of $25 to $35 million," said Lampley.

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The current record price for a Monet was a similar 1919 water lily painting that Christie's auction house sold in June 2008 for $80 million.

(Huguette Clark, pictured above, was shy, but not sad. Her friends and the few relatives who knew her describe her as cheerful, gracious, stubborn, and devoted to her art and her charity to friends and strangers. She poses in a Japanese print dress at about age 37. Source: The Estate of Huguette M. Clark, from the book "Empty Mansions."

The New York Times best-selling biography "Empty Mansions," co-authored by NBC News Investigative reporter Bill Dedman and Paul Clark Newell Jr., focuses on the reclusive heiress' life story, her personal fortune valued at over $300 million and the mystery surrounding her many estates that remained empty for much of her adult life. Photos of the Clark family have been provided courtesy of Dedman.

—By CNBC's Erica Emmich.

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