What is the legal ruling concerning a man who married his wife's younger sister after being informed of the death of his wife, who was unjustly imprisoned, and then it became clear that his first wife was still alive after her release from prison?

If a man marries his wife's sister believing his wife to be deceased, and then it becomes clear that she is still alive, his marriage to her sister is immediately annulled due to its inherent invalidity. His first marriage to his living wife remains valid, as it is forbidden to combine two sisters in marriage. If it becomes clear that his wife is alive after he has married her sister, he is not permitted to have intercourse with his first wife until her sister's 'iddah (waiting period) has concluded, so as not to combine the two sisters in intercourse, for a woman in 'iddah is considered to be like a wife.