Angad will come to know at the mandap itself as it is always shown in ekta 's serials that at the last moment when they are about to marry they come to know the truth.
as far as i feel angd will not marry mishti if he comes to know the truth because he had enough guts even to refuse mishti while the engagement day and even he was the first and the most eager person who wanted to talk to his mother abut kripa and himself but it was Kripa the idiot who always kept on refusing to tell his mom.
angad will leave the mandap and then he will go to dadi's house to meet kripa but he will come to know that kripa has faced an accident then following goes as it is shown in the promos.