Ils vivèrent un amour fou. -> They lived a passionate love.
French adjectives have a gender, matching the nouns they modify. For instance, the adjective ‘white’ in ‘a white armchair’ is masculine because ‘armchair’ – fauteuil – is masculine. However, the adjective ‘blue’ in ‘a blue chair’ is feminine because ‘chair’ – chaise – itself is feminine.
The general rule states that the mark of a feminine adjective is an E added at the end of its masculine form.
Feminine Adjectives take an E at the end of the masculine form:
un fauteuil bleu -> une chaise bleue