inconceivable

adj

1. Unable to be conceived or imagined; unbelievable.

   “While the world altered dramatically during the course of her reign, the monarchy did too, though rather more imperceptibly: the walkabouts that increasingly characterised royal appearances, the pop concerts at Buckingham Palace, the throwing open of the royal palaces to visitors – even the paying of income tax, and royal podcasts – would have been inconceivable as innovations at the time Elizabeth came to the throne.”