Cameron and Tyler Winklevoss, the twin brothers who became the world's first bitcoin billionaires have had their fortune slashed after the digital currency plunged this week.

The pair, who invested A$14 million ($15.3m) in bitcoin in 2013, saw their investment skyrocket late last year after bitcoin increased in value by 10,000 per cent, peaking at US$19,511 ($26,715).

However, the American brothers have now seen their fortunes drop 37 per cent in the past month after bitcoin dipped below US$10,000 this week, slicing US$443m ($607m) from the net worth of each brother, according to the Bloomberg Billionaire Index.

Last year the now ex-billionaires described the cryptocurrency as "better than gold".

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When compared to gold, bitcoin shares all the same nine foundational traits, including scarcity, durability and portability, and it matches or beats gold on all of these traits.

"We see bitcoin as potentially the greatest social network of all," said Tyler in 2016.

According to the Financial Times, the brothers viewed bitcoin as a missing piece of the digital economy that would change the way transactions are made.

The pair first learned of bitcoin while on holiday in Ibiza in 2012, and in 2015 they launched a digital currency marketplace, known as Gemini, that allows investors to buy, sell and store bitcoins.

"We wanted to build an exchange that was similar to Nasdaq or NYSE for digital currency," Tyler Winklevoss said at the time.

"We wanted something that both Wall Street and Main Street felt comfortable with."

"I remember when people said Facebook was a fad," Tyler told the Financial Times.

"We saw this movie play out already with Facebook. We feel like we're in the same movie again, just with a different cast of characters."

Don't feel too sorry for the pair though - they still each have US$739m, at least on paper anyway.