"They have sold more works of art than anybody alive."

That's a bold statement, but one to be believed when it comes from world-famous Christie's auctioneer Christopher Burge.

Burge was talking about the Nahmad family, an art-collecting dynasty renowned for its impressive stable of impressionist and modern works, including one of the largest collections of Picasso.

Modest beginnings in Milan

When the brothers began their collection, Juan Gris' work was undervalued. Today, the record for his work - held by Nature morte a la nappe a carreaux - stands at $57.1m

The story of the Nahmad art collection begins in Milan in the early 1960s, as banker Hillel Nahmad flees Beirut for the safety of his three sons, Guiseppe, Ezra and David.

Enjoying the high life in fashionable Milan, the teenage boys began to deal in art, led by their oldest sibling, Giuseppe, and would even skip school to trade on the Italian stock market, with their father's penchant for profit running strongly through their veins.

It was in 1960s Milan that the three brothers attended an exhibition of Juan Gris' art, arranged by renowned cubist and Picasso dealer Daniel-Henry Kahnweile. Here they bought two works - the only ones sold at the exhibit - from the soon-to-be top selling artist, whose potential had yet to be recognised.

Today, Gris' record at auction stands at $57.1m (pictured), making him one of the top selling cubist artists on the market. The Nahmads' eye for a money maker was apparent from the start.

Seeing their enthusiasm for the art world, Kahnweile befriended the brothers and soon began to enhance their art collection, selling them works by blue-chip artists such as Pablo Picasso and Georges Braque, as well as more from Juan Gris.

A global grip on the art market

Yet the Red Brigades' violent terrorism made Milan too dangerous for the Nahmads to stay, and the family prepared to move again. This time they would not go together, with Giuseppe and Ezra heading for Monaco, while David moved to New York - the collecting dynasty had gone global.

Using their knowledge of investing, combined with a passion for art, the brothers began to spread solid roots in their chosen cities. The pioneering Giuseppe, better known as Joe, is said to be responsible for discovering the likes of Lucio Fontana and commissioning works from Wifredo Lam during this period.

Finding opportunity in the saturated Paris market and reselling at a huge profit elsewhere using the family's global reach, Giuseppe also took advantage of economic downturns, buying several Picassos for around $40,000-50,000 in the 1970s.

It was this keen eye for profit that allowed Ezra to open his London gallery, while David opened his own in New York. Now firmly established in three of the world's luxury hotspots, the Nahmad brothers soon became the go-to dealers of choice for the world's collecting elite. 

According to Los Angeles' Museum of Contemporary Art's director, Jeffrey Deitch, the Nahmads run their company "like a major brokerage firm in the stock market", adding, "the market needs a force like this to function".

Continuing the legacy

Despite being the patriarch of the company, Guiseppe never got over the death of his older brother, Albert, who was killed in a plane crash in the 1950s. Described as once being "a big spender but now tight with himself and uncomfortable with happy people", Guiseppe had been in mourning for some time when he died in 2012.

With the Nahmads keen not to show any chinks in their art dealing armour, news of the death was not released in the media. Guiseppe had no children and never married, leaving only the two elderly brothers in charge of the world conquering dealership he had established.

In 2014, the management of the empire lies in the hands of David and Ezra's two sons - both named Hillel after their grandfather - who now manage their family's galleries in both London and New York.

Meanwhile, the legendary collection, which was briefly displayed to the public in 2011, resides in a tax-free warehouse close to Geneva's airport. The family has also put aside those works they consider to be "last-chance opportunities" - those that are so rare and valuable that, once sold, will not be seen on the market again in our lifetimes.

But will London Hillel and New York Hillel continue the Nahmad name with the fervour of their forebears?

"The whole art market probably has less turnover than one car company. At an educated guess, it's $15bn a year," London Hillel told the Financial Times. "The only thing you can take to the business to make it like manufacturing is contemporary art - which is limitless, and with that factory process you are making a luxury product.

"But people now are over the fact that they can buy something online and sell in a second, they are desperate to find meaning. There's real need for value and certainty."

So London Hillel is committed to furthering his family's interest, but the story in New York is not quite the same - NY Hillel had just been sentenced to one year in jail following his involvement with a sports betting ring that involved Russian organised crime.