Kristian Konstantinov Kostov was born on March 15, 2000 in Moscow, Russia to a Kazakh mother and a Bulgarian father. He has an older brother, Daniel, and a younger sister, Sofia. He has a very close relationship with his cousins. He even call them his siblings since the familys share living in Moscow.
He has both a Russian and a Bulgarian citizenship. He normally lives in Bulgaria in the summer seasons and the rest of the year in Moscow.