Wilder's first choices for Frank Flannagan were Cary Grant and Yul Brynner. "
It was a disappointment to me that [Grant] never said yes to any picture I offered him," Wilder later recalled. "
He didn't explain why.
He had very strong ideas about what parts he wanted".
The director decided to cast Gary Cooper because they shared similar tastes and interests and Wilder knew the actor would be good company during location filming in Paris. "
They talked about food and wine and clothes and art", according to co-star Audrey Hepburn, Wilder's only choice for Ariane.

Talent agent Paul Kohner suggested Maurice Chevalier for the role of Claude Chavasse, and when asked if he was interested, the actor replied, "I would give the secret recipe for my grandmother's bouillabaisse to be in a Billy Wilder picture".
Love in the Afternoon marked Chevalier's first non-singing role in a film since 1947.
The film was also the American feature film debut of character actor John McGiver.
Wilder's first choices for Frank Flannagan were Cary Grant and Yul Brynner. "It was a disappointment to me that [Grant] never said yes to any picture I offered him," Wilder later recalled. "He didn't explain why. He had very strong ideas about what parts he wanted". The director decided to cast Gary Cooper because they shared similar tastes and interests and Wilder knew the actor would be good company during location filming in Paris. "They talked about food and wine and clothes and art", according to co-star Audrey Hepburn, Wilder's only choice for Ariane.
Talent agent Paul Kohner suggested Maurice Chevalier for the role of Claude Chavasse, and when asked if he was interested, the actor replied, "I would give the secret recipe for my grandmother's bouillabaisse to be in a Billy Wilder picture". Love in the Afternoon marked Chevalier's first non-singing role in a film since 1947. The film was also the American feature film debut of character actor John McGiver.
Love in the Afternoon (1957 film)