In the Northern and Southern Dynasties when the State of Chen (A.D. 557-589) was facing its demise, Xu Deyan, husband of the princess, broke a bronze mirror into halves. Each of them kept a half as tokens in case they were separated. Soon afterwards, they did lose touch with each other, but the two halves of the mirror enabled them to be reunited.
“破镜重圆”这个成语比喻夫妻失散或分离后重新团聚。
This idiom is used to refer to the reunion of a couple after they lose touch or break up.