Which French writer wrote the novel "Bonjour Tristesse"?

Françoise Sagan (born Françoise Quoirez; 21 June 1935 – 24 September 2004) was a French playwright, novelist, and screenwriter. Sagan was known for works with strong romantic themes involving wealthy and disillusioned bourgeois characters. Her best-known novel was her first "Bonjour Tristesse" (1954) which was written when she was a teenager.

Sagan was born on 21 June 1935 in Cajarc (Lot) and spent her early childhood in Lot, surrounded by animals, a passion that stayed with her throughout her life. Nicknamed 'Kiki', she was the youngest child of bourgeois parents – her father a company director, and her mother the daughter of landowners.

The pseudonym "Sagan" was taken from a character (Princesse de Sagan) in Marcel Proust's "À la recherche du temps perdu" (In Search of Lost Time). Sagan's first novel, "Bonjour Tristesse" (Hello Sadness), was published in 1954, when she was 18 years old. It was an immediate international success. The novel concerns the life of a pleasure-driven 17-year-old named Cécile and her relationship with her boyfriend and her adulterous, playboy father.