Forbes estimates Durov’s net worth at $15.5 billion. Although born in Russia, he left the country in 2014 after resisting government pressure to release data about Ukrainian protest leaders from his previous social network Vkontakte. Durov now lives in Dubai, where Telegram is based, and his plane was reportedly flying in from Azerbaijan.

Durov said last month that Telegram had 950 million active users, with a goal of reaching 1 billion this year. At the same time, the company claims to have around only 30 engineers — a very small team for an app of Telegram’s scale, likely making Durov even more important to the company’s operation.