totally unexpected; completely unforeseen
A set phrase used when something happens entirely without warning or beyond prediction. Often carries a nuance of an accident or misfortune.
His death was completely unforeseen.
I lost my family in a totally unexpected accident.
A set phrase combining 不慮 (unexpected) with 外 (outside), literally 'outside of expectation'. The exact historical derivation is uncertain, but it functions as a fixed expression for something completely unforeseen.