From: Rabbi Moshe Sofer
To: Unknown recipient
A widow's mother-in-law claimed her late husband had a son from a previous marriage, which would bind the widow to yibum. The Chasam Sofer rules the widow is permitted to remarry, concurring with the Pri Megadim and Chavas Da'as. His primary reasoning is that the man lived in the community for fifty years without ever mentioning another son — not even in his will — establishing a strong chazakah that no such son existed, against which the mother-in-law's testimony and the elderly women's partial recollections are insufficient.
Source: Shu"t Chasam Sofer EH I §41