Probatio Diabolica

This expression could be used to describe what occurs when whoever claims a right or a situation, from which a legal consequence is derived, is unable to prove a specific fact or extreme, since it is in the hand of the other party to prove the opposite end of it.

This situation causes an alteration in the burden of proof that determines that, since it is not in the hands of the person who claims to prove this fact due to the impossibility of doing so, since its response depends on the party to whom the claim is made, it is in the "must" of this claimed party to verify it.