aurait pu arriver / aurait pu se produire
Best thing that could have happened to me, doctor.
La meilleure chose qui aurait pu m'arriver, docteur.
— Carandiru (2003)
I don't know what could have happened to it.
Je ne sais pas ce qui a pu lui arriver.
I don't know how this could have happened.
Je ne sais pas comment cela a pu arriver.
And that was the best thing that could have happened.
Et c'était la meilleure chose qui pouvait arriver.
— Central Station (1998)
It's true that everything could have happened as you said.
Il est vrai que tout aurait pu se passer comme vous l’avez dit.
— The Invisible Guest (2017)