Dictionary / Vocabulary / 腹心
ふくしん
one's confidant; trusted friend; trusted retainer
common word
汚い手で会社を乗っ取ったものの、腹心だと思っていた部下に裏切られ、因果応報だね。
When the trusted confidant of the person who conducted a hostile takeover of the company betrayed him, it was a sort of retributive justice.