Tech entrepreneur Elon Musk has again sold billions of dollars worth of Tesla shares after the expensive Twitter takeover.

In the past few days, sales have added up to around four billion dollars (around four billion euros), according to Tesla documents published by the SEC on Wednesday night. Reasons for the sale were not initially known. Musk is the boss of the electric car manufacturer Tesla and shares in the company make up the majority of his billion dollar fortune. He is considered one of the richest people in the world.

Musk acquired Twitter for around $44 billion. In addition to investing his own funds, he also took out loans of around 13 billion dollars. According to media reports, servicing these loans alone costs around one billion dollars a year. According to Musk, Twitter writes losses of around four million dollars a day. Recently, advertising revenues collapsed, as large companies such as Volkswagen and the pharmaceutical company Pfizer put their ads on the online service on hold. They want to wait and see how Musk’s Twitter will deal with offensive content such as hate speech, targeted false claims and conspiracy theories.

After a $8.5 billion sale in April, Musk sold Tesla shares worth around $7 billion again in August. He should have put the money into the Twitter purchase.

At the end of last year, Musk had already raised more than $16 billion by selling shares in the electric car manufacturer. He had to do this in part to pay taxes on redeemed stock options.