A real estate broker has filed a $21 million breach of contract lawsuit against former client Extell Development Co., alleging the corporation and other defendant entities failed to cough up the hefty commission after he brokered their acquisition of properties allegedly worth billions.

The Manhattan Supreme Court complaint alleges broker Austin Schuster—through plaintiff LLC the Austin Schuster Group—entered into a commission agreement in July 2015 with Extell and other related defendant entities.