unexpected

Not expected, anticipated or foreseen.

She was a fat, round little woman, richly apparelled in velvet and lace, […]; and the way she laughed, cackling like a hen, the way she talked to the waiters and the maid,[…]—all these unexpected phenomena impelled one to hysterical mirth, and made one class her with such immortally ludicrous types as Ally Sloper, the Widow Twankey, or Miss Moucher.

But the latest Santa Fe development, while not spurring the Rock Island to any further acceleration, has drawn fire from a totally unexpected quarter.

Someone or something unexpected.