quirk of fate

Translations
стечение обстоятельств
It was a quirk of fate that they met on the same train.
Это было стечение обстоятельств, что они встретились в одном поезде.
Definitions
A quirk of fate refers to an unexpected or unusual event or circumstance that significantly alters the course of events in a person's life, often in a surprising or ironic way.