Billionaire investor Carl Icahn scored a $250 million gain on Twitter stock by calling Elon Musk's bluff

• Carl Icahn piled about $500 million into Twitter in recent months, The Wall Street Journal said.

• The Icahn Enterprises chief has likely notched a $250 million gain on the social media stock.

• Twitter shares surged 22% on Tuesday after Elon Musk offered to complete his buyout of the company.

Carl Icahn has scored an estimated $250 million gain on Twitter stock by calling Elon Musk's bluff.

The billionaire investor and Icahn Enterprises chairman plowed about $500 million into the social-media company in recent months, The Wall Street Journal reported on Tuesday. He bought the shares in the mid-$30s, sources told the newspaper, suggesting he purchased around 14 million shares or close to 2% of the business.

Tesla CEO Elon Musk agreed to buy Twitter for $54.20 a share in April, sending its stock price towards that level. However, he tried to back out of the deal over the next few months, prompting a lawsuit and sending Twitter shares down again. As a result, Icahn was able to buy them at a steep discount to Musk's offer.