Billionaire Elon Musk joined President-elect Trump’s call earlier this week with Ukrainian President Volodymyr Zelensky, a sign of how Musk’s close relationship with Trump could manifest itself as he prepares to take the White House.

Elon Musk was with Donald Trump at Mar-a-Lago when the president-elect spoke with Ukraine’s leader. It is not clear if they discussed any change in U.S. policy toward Ukraine.

The billionaire owner of SpaceX was on the call briefly and his involvement wasn’t planned, according to those familiar with the conversation.