Through chance.

synonym: perchance.

Roget 621: randomly, by chance, fortuitously; unpredictably, unforeseeably; casually etc. 156; unintentionally etc. adj.; unwittingly.    en passant [Fr.], by the way, incidentally; as it may happen; at random, at a venture, at haphazard.    ... show more

By accident.

synonyms: by luck, haply.

Without advance planning.

synonyms: accidentally, circumstantially, unexpectedly.

Roget 156: by chance, accidentally, by accident; casually; perchance etc. (possibly) 470; for aught one knows; as good would have it, as bad would have it, as luck would have it, as ill-luck would have it, as chance would have it; as it may be, as it may chance, as it may turn up, as it may happen; as the case may be.    ... show more