SoftBank shares tank near 19%, wiping off $4.6 billion from founder Masayoshi Son's fortune

SoftBank Group shares tanked nearly 19% on Monday amid a global sell-off, wiping off billions of dollars from founder Masayoshi Son's fortune.

Shares of the Japanese giant, known as one of the world's largest tech investors through its massive Vision Fund, have slid since last Thursday as Japanese equities began to fall after the Bank of Japan raised its benchmark interest rate.

On Monday, Son's net worth fell by $4.6 billion alone, according to the Forbes real-time billionaires list.

The Nikkei 225 meanwhile posted a 12.4% loss that marked the worst day for the index since the "Black Monday" of 1987.

Before the declines of the past few days, SoftBank's stock had rallied this year and even hit a new record high, as the company's Vision Fund division continued its recovery. A big jump in the share price of Arm, the British chip designer that is roughly 90% owned by SoftBank, has also contributed to the Japanese company's stock appreciation this year.

But Monday's price plunge leaves SoftBank's shares just 1.7% higher for the year. About $28.3 billion has been wiped off SoftBank's value since the close of trade on Wednesday, according to CNBC calculations.

SoftBank will report its fiscal first-quarter earnings on Wednesday, with investors hoping to see further recovery in the Vision Fund.

Son, who has been out of the public spotlight for a while, made a reappearance in June to discuss his vision for the future of artificial intelligence, which he predicts will eventually be 10,000 times smarter than humans.