SoftBank Group Founder and Chief Executive Masayoshi Son, already one of Asia's richest men, may have just added billions into his pocket from Thursday's trading session.

SoftBank's stock ended Thursday's session in Japan at 9,962.0 yen per share, a 17.73 percent gain over its last close at 8462.0.

Son owned 231,205,000 shares in the Japanese conglomerate as of Sept. 30, 2018, according to the company's website. If that number is still accurate, then that would mean Thursday's stock move made Son about 346.81 billion yen ($3.15 billion) richer.