adverb
unexpectedly; by chance; by accident
Expresses that something happened without prior planning or intention, often with a nuance of surprise or coincidence.
図らずも彼と同じ電車に乗り合わせた。
Unexpectedly, I ended up on the same train as him.
図らずも秘密を知ってしまった。
I accidentally found out the secret.
偶然 is a more common and neutral word for 'by chance' or 'coincidence', while 図らずも carries a stronger nuance of something happening contrary to one's intentions or expectations.
思いがけず also means 'unexpectedly', but it emphasizes the speaker's lack of anticipation, whereas 図らずも often implies that the event was not planned or intended by anyone involved.
Derived from the negative form of the verb 図る (はかる, 'to plan') with the particle も, literally meaning 'without planning' or 'unintentionally'.