ざるを ない
zaruo enai

i-Adjective
Expression

1. have to; have no choice but to; cannot help (doing); be compelled to; be obliged to; be forced to

わたくし本当 ほんとのことを わざるを なかった。
watashiwa hontōno kotō iwazaruo enakatta.
I couldn't but speak the truth.