inconcevable

Il m'est inconcevable qu'il fasse une chose pareille.

It is inconceivable to me that he would do such a thing.

Il est inconcevable que tu parles au téléphone tandis que tu es derrière le volant.

It's inconceivable that you would talk on the phone whilst behind the wheel.

Il a commis des crimes inconcevables.

He committed inconceivable crimes.

Par une contradiction inconcevable, il ne pardonnait pas à la jeune fille d’avoir suivi ses ordres.

By an inconceivable contradiction, he did not forgive the young girl for having followed his orders.