一朝天子一朝臣

yīcháotiānzǐyīcháochén
  1. new emperor, new officials (idiom)
  2. a new chief brings in new aides

CEDICT

When a leader falls from power, his/her subordinates may fall from power too.

Wiktionary

（諺語）新的帝王登基，舊朝的臣僚便為新朝的臣僚所取代。泛指主事者一旦更換，從屬也隨之變動。含有任用親信、私人的貶損之意。

重編國語辭典

Entry Composition

1 一朝 yīzhāo
  1. (literary) one day; unexpected occasion in the future
  2. one day; unexpected occasion in the future
2 天子 tiānzǐ
  1. the (rightful) emperor
  2. "Son of Heaven" (traditional English translation)
3 一朝 yīzhāo
  1. (literary) one day; unexpected occasion in the future
  2. one day; unexpected occasion in the future
4 臣 chén
  1. state official or subject in dynastic China
  2. I, your servant (used in addressing the sovereign)
  3. Kangxi radical 131