Source : Webster's Revised Unabridged Dictionary (1913)

Cruelly \Cru"el*ly\, adv.
   1. In a cruel manner.

   2. Extremely; very. [Colloq.] --Spectator.

Source : WordNet®

cruelly
     adv 1: under cruel circumstances; "a cruelly bitter winter"
     2: in a cruel manner; "he treated his students cruelly"