Unendurably

adv. [UN-¹ 11: cf. prec.] In an unendurable manner or degree.

1832.  Southey, Hist. Penins. War, III. 103. That sovereignty … would become unendurably tyrannical.

1867.  Augusta Wilson, Vashti, xxvii. My ardent lover would be too unendurably miserable separated from me.

1890.  ‘R. Boldrewood,’ Col. Reformer (1891), 177. The routine life … would be unendurably dull.