UnendingMasquerade

A young man and a young woman, two youthful lovers - Raoul and Marguerite - each receive a secret letter, stating that the other is cheating on them: if Raoul wishes to verify this he needs but to go to the oncoming masked ball; his beloved will be there, dressed as a Congolese Kano. The girl receives a letter of the same type: go to the ball, your beloved will be there, disguised as a Harlequin.

Well then. The evening of the ball, two figures can be seen boring themselves to death and leering at each other from behind their masks: a Congolese Kano, and a Harlequin...

Finally, he approaches her, and asks her to dance. It ends in a private quarter, where they storm at each other and rip each other's masks off; and then - peak of consternation - the story concludes:

the Harlequin, was not Raoul...

the Kano, was not Marguerite...

After which the two young lovers agree never to quarrel again!

And that's the story, called Un Drame Bien Parisien.

Can be found (in French) in the book À Se Tordre by Alphonse Allais.