Cosmetics billionaire Leonard Lauder, heir to Estee Lauder, bequeathed a jaw-dropping collection of rare Cubist art, which Forbes values at $1.1 billion, but the Metropolitan Museum of Art in New York City is staying mum on the value of the 78 pieces.

Lauder, 80, donated works from Pablo Picasso, Georges Braque, Juan Gris, and Fernand Léger, from "one of the foremost collections of Cubism in the world," the Met said.

It's one the largest donations ever to the Met, said Maria Di Mento, staff writer with the Chronicle of Philanthropy. Whether it's the largest and what it's worth is a subject for speculation.

(Image credit: Metropolitan Museum of Art/AP Photo)

In 2002, philanthropist and publisher Walter Annenberg bequeathed about $1 billion worth of paintings to the Met upon his death. A collector had reportedly once offered $1 billion for Annenberg's 53 Impressionist and Post-Impressionist paintings.

"Even though the artwork from Lauder and Annenberg are major, major works, it's still gets really tricky when you start talking about the value of an artwork because it can change over time," Di Mento said. "If a museum has come out and said their experts and curators who specialize in this art say a value, then that's a strong endorsement, but rarely do museums do that, especially the Met," Di Mento said.

Brian Roughton, Heritage Auctions' Director of American and European Art, said Lauder's collection is priceless, and wouldn't be surprised if he read a "sensational" headline valuing the collection at $2 billion.

"When they give a value of a collection, the biggest problem with something like that is most of these paintings are irreplaceable," Roughton said. "It would be difficult to ascertain a true value."

These are also premiere works from the most sought-after artists, examples of which seldom come on the market. And museums throughout the world are loathe to talk about art in terms of dollars, as was the case with the Met.

One of Picasso's most expensive works of art, "Nude, Green Leaves and Bust (1932)," sold for more than $106 million, at a Christie's auction in 2010.

A spokeswoman for the museum declined to comment about the value of Lauder's collection nor reveal what the most valuable collection or piece of art at the museum.

In 2004, a New York Times article stated that the "Madonna and Child" painting by Duccio di Buoninsegna, bought by the Met for more than $45 million, was the most expensive ever purchased by the museum.

In a book published in 2009, author James R. Houghton claims "Wheat Field with Cypresses [by Van Gogh] remains the "most expensive single work of art" ever purchased for the museum. The book is called, Philippe de Montebello and the Metropolitan Museum of Art: 1977-2008. The piece was donated by none other than Walter Annenberg, who said he paid $57 million for the piece.

The Met is the largest museum in the U.S. and among the three largest in the world, with over two million art objects and two million square feet of space. What's it all worth?

Like the MasterCard ad says, it's priceless.