A litigant who knows a halakhic source against himself

Is a litigant who has found a strong halakhic source against himself obliged to disclose what he knows to the judges? I thought to myself that it was clear that he was, otherwise he was just a thief, but I heard an old bar-orian from my extended family who said that in his opinion it was a fact and he knew the dayan's method on the subject which is based on an interpretation of the Yerushalmi by virtue of a question, and that same bar-orian who was a judge had another Yerushalmi who sheds light on the first Yerushalmi, which I am saying is a certain place in his opinion in the second Yerushalmi and not according to the halakhic law, so that the renewed interpretation is not needed, and he did not reveal it to the dayan, and the law ended up in favor of that dayan, and according to him, after the rabbinic court ruled, then certainly the money in his hands is kosher money, and moreover, the opinion of people to buy and sell depends on the opinion of the dayanim as it is, and after years he saw that that dayan had found or was told the second Yerushalmi and indeed he retracted it. Whether the act itself was or was not, I do not know, the man is already old and his stories become strange over the years, but the idea is interesting, is there such a side that a lawan would hide a source or halachic reasoning that he sees that the dayanim do not Do you know?