After the Second World War, when Adolf Hitler was officially declared dead, the Allied Forces concluded that his estate was pretty modest by dictatorial standards—worth about $800,000 in today’s money.

He had always claimed to have no interest in money, and in his will, declared: “What I own belongs, as so far as it is of any value at all, to the party.” The truth could hardly have been more different; it is now claimed that he had amassed a personal fortune in property, art and cash worth in excess of $6 billion.

When he wasn’t plotting his ascent to power in Germany and subsequent European domination, Hitler was working on an incredible array of money-making schemes. He surreptitiously pocketed collections from his rallies, channeled millions into personal accounts through government purchases of his book and secured a slew of image-rights deals that put LeBron James to shame.

It wasn’t only the adoring crowds that had no idea of his profiteering; the German taxman were also kept in the dark. By the time he was chancellor he owed $3 million in taxes, according to a British television documentary. Soon afterwards it was quietly decided that chancellors need not pay tax.

“He felt that paying taxes was beneath him,” explained Cris Whetton, author of the book Hitler’s Fortune. “He loved money. He just wasn’t prepared to do much work for it.”

The British TV documentary, The Hunt for Hitler’s Missing Millions, asks what happened to the fortune. “By the time we get to 1944 he’s definitely in the billions of reichsmarks. It would not be far off billions of Euros today. From virtually bankrupt to billions in less than a decade,” says Whetton.

A lot of the cash was sunk into property, with Hitler spending the equivalent of more than $200 million renovating his countryside retreat, Berchtesgaden, into a sprawling 30-room complex, replete with Persian rugs, tapestries and Old Masters.

Godfrey Barker, an art historian, said Hitler’s appreciation for fine art helped him to amass a stunning personal collection worth hundreds of millions of dollars. “Hitler the man who wanted to rule the world was only the public face,” Barker told the program. “The private man is something that few people seem to understand. His beating heart was all to do with art. He held dinner parties at Berchtesgaden at which art was freely discussed with visiting generals and not a word is spoken about the blood spilt in the camps within 50 miles. Dacau, the village south of Munich which housed one of the filthiest concentration camps, was a place where Hitler housed art.”

He estimated that around 3,000 of Hitler’s collection of 8,500 paintings were worth millions of dollars each.

The Nazis were notorious for looting art as they rampaged through Europe in the 1930s but Whetton said he was astonished to discover that this did not seem to be the source of Hitler’s collection. “I had expected to find that he was directly responsible for the looting and stealing of paintings he wanted for himself and I couldn’t find any evidence for it. I found evidence that he paid for them—sometimes at knockdown prices, but not direct theft,” he said.

Certainly, Hitler had the cash on hand. His friend Max Amann, the publisher of Mein Kampf, was channeling back 10 percent royalties on millions of copies of the book, many of which were bought up by the German government. Hitler was also receiving millions through Heinrich Hoffmann, his official photographer since the 1920s, who came up with the idea of licensing his image for a fee, including for payments for every stamp minted by the government.

According to documents that were declassified decades later, an investigation by OSS, a precursor to the CIA, found accounts worth over $350 million in the 1940s. That money was never accounted for after the war.

Kenneth Yormark, forensic accountant based in New York, says its whereabouts is still a mystery. “Hitler’s bank accounts are not very well known,” he said. “There’s not a lot of information that’s out there.”

Hitler’s sister spent the last 12 years of her life fighting to access the inheritance due to her. Her right was granted in 1960, four months before she died, but she was seemingly unaware of the vast fortunes that had been stashed away.

Yormark said there had been evidence of accounts in Switzerland and Holland but they had never been disbursed to Hitler’s heirs. “They would potentially have the right to attempt to try and claim some of those funds,” he said. “Theoretically, the bank should have tried to find the rightful owner.”

He said it was likely that the Swiss government would have collected any unclaimed cash in the accounts by now.

Hitler’s will, which was written in his bunker shortly before he killed himself, was discovered by a specialist German-speaking British Army unit. Herman Rothmann, a German-Jewish refugee who fled to Britain and signed up to join the army at the age of 18, was there when one of Hitler’s press aides was captured.

“In our unit there was a man, he saw immediately there was something wrong. The shoulder pads didn’t look right,” he said. Hidden inside they found folded sheets of paper: “We were absolutely shocked when we saw the signature ‘Adolf Hitler’—it became evident that this was an extremely important document.”

For the most part, the Allies accepted that the document, which described his “modest estate,” was relatively accurate. Rothmann, now 89, said Hitler’s subterfuge had failed in the end. “He wanted to show his ambition purely for the German people,” he said. “A man like that wanted to project that image for eternity.”

The Hunt for Hitler’s Missing Millions is available to stream on Channel 5 in the UK.