fortuitous event

noun

for·​tu·​i·​tous event

fȯr-ˈtü-ə-təs-, -ˈtyü-

: an event of natural or human origin that could not have been reasonably foreseen or expected and is out of the control of the persons concerned (as parties to a contract) : force majeure

called also cas fortuit

see also frustration compare inevitable accident