Renaissance Technologies, a US hedge fund, may have earned more than $1.5 billion in two months by buying a Tesla shares(TSLA), which happened before the automaker's shares doubled this year.

Renaissance Technologies acquired 3.3 million TSLA shares last quarter, according to Form 13G. Since the beginning of the 4Q, Tesla shares have risen sharply, adding nearly 250% in value. According to the statement, at the end of 2019, Renaissance Technologies owned more than 3.9 million shares of the automaker.

Last quarter, the company's shares cost Renaissance Technologies about $1.6 billion (the price of one share was $418). The fund owns a stake in Tesla in the amount of 3.9 million shares. Considering that the automaker’s shares are currently trading at around $850 per share, the stake is worth about $3.3 billion.

The rally, in which Tesla almost caught up with the combined market capitalization of three of the large automakers General Motors, Volkswagen and Fiat Chrysler, which cost about $157 billion, perplexed some investors and analysts who said the company’s fundamentals weren’t strong enough to support the surge .

The company's shares are now trading at $843.5 per share, which gives it a market capitalization of more than $155 billion.

Renaissance Technologies is respected in the hedge fund industry for its reputation, although the firm is decidedly secretive. The quarterly disclosure of stock information for hedge fund managers, known as form 13F/G, is one of the few public ways to keep track of what they sell and buy.

Renaissance Technologies is a hedge fund founded in 1982 by mathematics professor Jim Simons, who decrypted Soviet codes during the Cold War. He specializes in stock trading using mathematical and statistical analysis models. Simons managed the hedge fund until 2009. The CEO of Renaissance Technologies is Peter Brown.