Larry Ellison has disclosed a $1-billion stake in Tesla.

The 10-figure holding was revealed in a filing with the US Securities & Exchange Commission.

The Oracle 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 $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.