"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」