The SEC filing said the Crown Property Bureau, which manages the multi-billion dollar assets of the royal family, had reduced its shares in Siam Commercial Bank by 3.33 percent on October 2.
That stake is worth 16.9 billion baht ($505 million) based on Friday’s closing share price of 151 baht.
The beneficiary of the shares was not specified but the move was carried out on the King’s behalf, the filing said.
The CPB, who now has a 18.14 percent stake in the bank, did not immediately respond to requests for comment.
The opaque agency does not declare its wealth but analysts estimate it manages between $30-60 billion in assets, making Thai royals among the richest in the world.
The CPB’s financial portfolio ranges from massive property ownership to investments in major companies, such as Siam Commercial Bank and Siam Cement Company.
Like all things regarding Thailand’s secrecy-shrouded monarchy, scrutiny of the CPB is curbed by a draconian defamation law that shields the royal family from criticism.
The transfers come after legal amendments passed in July gave King Maha Vajiralongkorn, who took the throne one year ago after the death of his father, direct control over a committee that oversees the CPB.
Under the previous law, the committee’s chairman was the finance minister, a move meant to ensure some semblance of government oversight.
The move was the latest in a series of steps by the new monarch to consolidate his control over the palace bureaucracy.
All media based in Thailand must self-censor when reporting on the monarchy to avoid violating the lese majeste law.