Larry Ellison has disclosed a US$1 billion stake in Tesla Inc. (TSLA.O

The 10-figure holding was revealed in a filing with the U.S. Securities & Exchange Commission. The Oracle Corp. founder and long-time friend of Tesla chief executive officer Elon Musk joined the electric car maker’s board in December in an effort to show regulators that the board is providing effective oversight.

Ellison, 74, is the world’s ninth-richest person with a net worth of US$51.4 billion on the Bloomberg Billionaires Index. He indirectly owns 3 million shares through the Lawrence J. Ellison Revocable Trust.

Ellison said Tesla was his second-largest investment in October without being more specific.