When the richest man in the world, Elon Musk, updated his Twitter bio on Friday — simply adding the word "Bitcoin" — it was followed by a near-immediate 13% increase to the Bitcoin (BTC) spot price.

Musk’s bio appeared to be updated on Friday morning and was followed by a cryptic tweet that referred to the inevitability of... something.

Tweeted at 8:22 am UTC, Musk’s 43 million followers apparently took notice. Some assumed the tweet was a reference to the Dogecoin (DOGE) price surge that was ignited by r/Wallstreetbets traders as a follow-up to the recent GameStop stock short-squeeze. Others assumed the tweet was related to Bitcoin.

Either way, at 8:24 am, Bitcoin suddenly took off. Over the course of the next 30 minutes, the value of Bitcoin increased by 13.9% as the coin price climbed from a starting point of $32,194. By 9:04 am, the coin was worth $36,670, according to data from CoinMarketCap. Shortly afterward, BTC continued to climb, eventually hitting $37,420 — representing more than 20% growth from the previous 24 hours.

In December 2020, the value of Dogecoin increased by 25% after Musk posted a Doge meme. Musk had previously posted Dogecoin memes followed by the words “It’s inevitable,” perhaps providing a clue to the nature of Friday’s tweet.

Musk isn't even the first billionaire to add the word "Bitcoin" to his Twitter bio. The social media site's own CEO, Jack Dorsey, did the same thing in mid-2020. Dorsey is the CEO of Square, the fintech company responsible for Cash App, which also caters to Bitcoin users. Almost 80% of Cash App's revenue came from Bitcoin alone by the third quarter of 2020.