winner/s

___________ of the 1960 Palme d'or at the Cannes Film Festival, Fellini's La Dolce Vita became a worldwide success.

a) A winner
b) The winner

Can there be one winner in the Festival? If so, I think (a) is the choice.

I think there can be only one winner, so it should be choice (b).

Am I correct? I wonder.

Many thanks.