In January, 2014, Tyler and Cameron Winklevoss each bought a ticket to travel to the edge of space on Virgin Galactic.
They bought them with bitcoin.
"I won't make that mistake again," Tyler Winklevoss tweeted Thursday.
That's because the price of a single bitcoin at the time was $800, Winklevoss said. On Friday, bitcoin is trading at $9,914.66 as of 3:57 p.m. EST, according to CoinDesk.
A Virgin Galactic ticket is valued at $250,000, according to Reuters. At that price Tyler would have spent roughly 312.5 bitcoin on his ticket, which today would valued at nearly $3.1 million.
TWEET: In January 2014, I bought a ticket to space on @virgingalactic with bitcoin.
The Winklevosses bought tickets on Virgin Galactic's spacecraft because they saw an inspiring parallel between the innovation of bitcoin, in which they are major investors, and space travel, with both "writing the next chapter in our history books," Tyler wrote in a blog post for Winklevoss Capital.
In February, Virgin Galactic took three test passengers to the edge of space and back in a supersonic test flight. In May, it completed a second successful test flight. Virgin Galactic previously told CNBC it was aiming to take paying customers, like the Winklevosses, to space starting in 2019, however, the company did not immediately respond to CNBC Make It's request for an update.
In his space tweet, Tyler likened his use of bitcoin for his Virgin Galactic ticket to a "Bitcoin pizza moment."
That's in reference to Laszlo Hanyecz, who in 2010 traded 10,000 bitcoin for two pizzas. At the time, bitcoin was worth less than one penny, "60 Minutes" reported. Now, 10,000 bitcoin would be worth over $99.2 million.
Tyler and Cameron Winklevoss are perhaps most famous for accusing Mark Zuckerberg of stealing their idea for a social network and winning a $65 million settlement with Facebook.
But the 37-year-old twins, who graduated from Harvard and were Olympic rowers, have also become vocal supporters of cryptocurrency. They co-founded a cryptocurrency exchange called Gemini and are the subjects of a book, "Bitcoin Billionaires: A True Story of Genius, Betrayal, and Redemption," out Friday.
The Winklevosses gifted Virgin Galactic founder Richard Branson a copy of the book, with a note that reads: "You are a true entrepreneur and visionary. We will never forget buying our ticket to space on Virgin Galactic with bitcoin. To the moon!"
See also:
Richard Branson's Virgin Galactic reaches space again, this time with first test passenger
Winklevoss twins: 'We need to be frenemies' with Facebook now that it's into Libra crypto
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This story has been revised.