Elon Musk kicked off a Tuesday presentation at Tesla’s Shanghai plant by tearing off his blazer and dancing enthusiastically to a song by his girlfriend, pop star Grimes. The eccentric CEO and founder has a multibillion-dollar reason to be in such high spirits.

Tesla stock has spiked since the company revealed last week that it delivered a record 112,000 vehicles in the fourth quarter, modestly exceeding the consensus estimate among analysts, and announced that its first full-scale production plant outside the U.S.—in Shanghai, China—is now delivering vehicles.

Shares surged 13% in the week through January 9—boosting Musk’s net worth by $2.1 billion, to $28.8 billion. The 49-year-old billionaire is currently the 34th-richest person in the world. Musk owns nearly 22% of Tesla’s stock, which accounts for roughly half of his fortune. He also has an estimated $12.5 billion stake in SpaceX, his privately held aerospace company known for reusable rockets.