by chance; coincidentally; as it happens
Used when something happens unexpectedly or without planning, often with a nuance of fortunate or surprising coincidence.
偶然にも、同じ電車に乗り合わせた。
By chance, we happened to be on the same train.
偶然にも、彼の誕生日に再会した。
Coincidentally, we met again on his birthday.
Derived from the noun 偶然 (coincidence) with the adverbial particle にも, forming a set phrase meaning 'by coincidence'.