May 2013. A Swedish count, who made his fortune in securities, settles a deal. The sum that changed hands is unknown, but the count can certainly afford it - he's one of the world's richest men.

The philatelic world breathes a sigh of relief: the Treskilling Yellow is back in the hands of a genuine collector.

The Treskilling Yellow - the world's most valuable stamp ever sold

Gustaf Douglas, a businessman, politician and nobleman, leaves the room triumphant. One of the most famous philatelic gems is now in his custody, and his name is added to the list of the stamp's illustrious owners.

His place in the history of stamp collecting is assured…

What's more, he's earned the right to call the Treskilling Yellow his own.

An expensive mistake

The Treskilling Yellow (or "three-skilling" yellow) was born when Douglas' home nation first issued its own postage stamps back in 1855, with a set of five values each showing the Swedish coat of arms. Denominated in Swedish skillings, the currency of the time, the three-skilling was to be printed in blue-green, while the eight-skilling sported a yellow hue.

As far as the post office was concerned, the printing was a success, yet one stamp escaped its scrutiny: a three-skilling stamp was printed in the yellow shade of the eight-skilling.

As it was intended - the treskilling blue-green stamp

It's not clear where the error was made, but it is thought that a damaged printing plate for the eight-skilling stamp was mistakenly replaced with a three-skilling. So far, just one stamp with the colour error has ever been discovered.

A forgery?

Years passed and no-one noticed the error had even been created. During this time, even the Swedish currency was changed, with stamps now denominated in "ore".

Then, in 1886, as stamp collector Georg Wilhelm Bachman went rifling through his grandma's attic in search of covers for his collection, he came across the three-skilling stamp in an unusual shade.

Soon, dealers and philatelists were falling over themselves to take the used stamp off Bachman's hands. A young collector, he was easily lured into a deal, settling for just seven kronor from Stockholm dealer Heinrich Lichtenstein.

The stamp changed hands between several of Sweden's most prominent collectors, until Sigmund Friedl, one of the most famous Austrian philatelists and a renowned forger of rare stamps, sold it for 4,000 Austro-Hungarian gulden to collector Philipp von Ferrary in 1894 - perhaps the best-known philatelist to have lived, famed for owning the world's largest collection of stamps.

One of Friedl's famous forgeries

It is with Friedl that questions surrounding the stamp's authenticity first appeared. The Austrian's chequered history casts doubt on any sale in which he was involved. These fears were remedied in the 1970s, when the Swedish Postal Museum claimed the stamp was a forgery, but later found it to be genuine through two different commissions.

For now, however, the stamp was held by Philipp von Ferrary, the incredibly wealthy son of the Duke and Duchess of Galliera. Ferrary's collection also contained the 1856 British Guiana 1c Magenta, the only 1851 2c Hawaii Missionary cover, and the only known cover featuring both values of the Mauritius Post Office stamps.

Quite simply, the finest collection the world has ever known.

Philipp von Ferrary, the greatest stamp collector the world has ever known

When Ferrary died in 1917, his illustrious amassment was donated to the Berlin Post Museum, where it was displayed until the end of the first world war, before being seized by France as part of German war reparations.

Ferrary had given the museum an endowment to care for his collection, hoping the collection would stay together forever. However, the French sold his albums bit by bit, in a series of auctions that are now part of philatelic history.

The Treskilling Yellow was bought by Swedish Baron Eric Leijonhufvud for £694 in the early 1920s, who sold it on for £1,500 in 1926 to Claes A Tamm, a Stockholm engineer who needed it to complete his entire Swedish collection.

Once Claes had had his fill, it was passed to a Swedish lawyer by the name of Johan Ramberg in 1928 for £2,000 (around $15,000 at the time).

Ramberg possessed every bit of the scrupulous personality required of lawyers, and managed to track down the Treskilling Yellow's original owner Georg Wilhelm Bachman, who had become a lieutenant colonel in the Swedish army.

He persuaded Bachman to given a detailed affidavit to the Swedish courts in 1931, which details his discovery and subsequent sale of the stamp - no doubt a moment he did not want to relive, given the stamp's newly discovered value.

However, Ramberg also had the stamp re-perforated along the top edge, forever erasing the original condition of the stamp. It also bears a slit in one of the corners, which was apparently present upon Bachman's discovery.

Nonetheless, the Treskilling Yellow was about to enter the golden period of its life, which would truly cement its reputation as one of the world's rarest and most desirable stamps…

She 'lifted up her dress'

The stamp next appeared in 1937 at London auction house HR Harmer, where it was sold to King Carol II of Romania. Nicknamed "The Playboy King", Carol was renowned for his extravagances, and paid £5,000 (over $30,000 today) to call the Treskilling Yellow his own.

King Carol famously fled Romania in a train laden with the nation's crown jewels, which he subsequently sold to fund his sumptuous lifestyle

King Carol II's lavish collection extended far beyond stamps, with a pair of pearl earrings that he once gave to his mistress selling for $2.5m at a UK auction house in 2012.

Towards the end of his life in 1950 (the king would die in exile in 1953), Carol sold the stamp to Rene Berlingen, one of Germany's foremost stamp collectors, who paid an unknown amount before the yellow gem was displayed at the Anphilex 71 convention in New York.

After Berlingen failed to sell the stamp at Anphilex, Stanley Gibbon's Steven Kander is said to have been given the stamp to sell on Berlingen's behalf, though how he got it is a story in itself.

One day at the company's headquarters in London, a young woman asked for Kander at reception. When he met the pretty customer in a private room intended for the most prestigious clients, she, according to Kander, quietly "lifted up her dress and underneath there was an old-fashioned petticoat into which was sewn on the inside, a special pocket".

From that pocket came the Treskilling Yellow, the elaborate get-up created to conceal the precious stamp from the pickpockets of London. Yet still it did not find a new home.

The stamp next appeared in 1974 at the Stockholmia 74 exhibition, which is where the Swedish Postal Museum first began to claim the stamp was a fake, believing it be either a fake of the original (which they also considered to be a fake) or a bleached eight skilling stamp reprinted with the three skilling image.

Rene Berlingen was forced to pay for a detailed report to prove the stamp's authenticity, and would never make a penny from its sale as it was later used to settle his enormous debts.

A record breaker

Here, the second "golde