unknownly

adverb2

1. •
   (rare) Obscurely, without being known or noticed.

   • Attentively the grey horse wended / (by many a mighty fist forfended) / through men that lay unknownly dying, / and trod on shallow blackened grass. — 1960
2. •
   (old-fashioned, rare) Mysteriously, without a known reason or cause.

   • Just then it open’d; and th’enclosed Grain / Unknownly vanisht; and then clos’d again — 1646