Webster's Revised Unabridged Dictionary · 1913

Kingly

Kingly , adjective

Belonging to, suitable to, or becoming, a king; characteristic of, or resembling, a king; directed or administered by a king; monarchical; royal; sovereign; regal; august; noble; grand.
Kingly magnificence. — Sir P. Sidney
A kingly government. — Swift
The kingly couch. — Shakespeare
The kingliest kings are crowned with thorn. — G. Massey
Leave kingly backs to cope with kingly cares. — Cowper

Kingly , adverb

In a kingly or kinglike manner. — Shakespeare
Low bowed the rest; he, kingly, did but nod. — Pore

Although this citation, one from Paradise Lost, and one from Shakespeare's ll4th Sonnet are given by lexicographers as examples of adverbial use, it is by no means clear that the word is not an adjective in each instance.