"I was shocked when a nice co-worker suddenly had to transfer.
"I was shocked when a nice co-worker suddenly had to transfer. "I was shocked when ~" 「〜てショックだった」 "a nice co-worker" 「親切な同僚」"a friendly co-worker" や "a nice colleague" も言えます。 "suddenly" 「急に」"all of a sudden" も使えます。 "had to transfer" 「転勤することになって」