Deadline.The Emmy winner will star alongside Bradley Cooper as Bernstein, who will also direct, as his follow-up to his 2018 hit A Star Is Born.Gruen wrote the 1968 authorized biography The Private World of Leonard Bernstein with Ken Heyman, while he was working as a journalist in New York.He wrote for the New York Herald Tribune and the New York Times as an art critic, and also wrote biographies on composer Gian Carlo Menotti, Keith Haring and his own autobiography, Callas Kissed Me...Lenny