Is it obligatory to inform a brother's wife of his intention to marry secretly, knowing that he refuses to leave her and affirms his love for his first wife?

It is not advisable to inform the brother's wife of his desire to marry another woman, nor is it obligatory for a husband to inform his wife of his marriage to another. However, he must act justly between his wives. What the brother did by forming a relationship with a woman until she sought a divorce to marry him is a heinous reprehensible act, as instigating discord (takhbib) is one of the gravest forbidden acts. The brother must repent to Allah.