A more thorough explanation:

The last-in-time-marriage presumption is a legal concept in family law that assumes the most recently contracted marriage is valid. This presumption usually applies in situations where a person remarries, believing they are divorced, but their former spouse claims there was never a valid divorce.

For example, let's say John and Jane were married, but they separated and John moved to a different state. John filed for divorce in his new state, but Jane never received the papers and didn't respond. John assumed the divorce was granted and remarried. Later, John dies, and his new spouse claims his pension benefits. However, Jane comes forward and says the divorce was never valid because she never received the papers. In this case, the last-in-time-marriage presumption would apply, and Jane would have to prove that there was no valid divorce.

The last-in-time-marriage presumption is used to determine which marriage is valid when there are multiple marriages or claims to benefits. It places the burden of proof on the party claiming that a previous marriage is still valid.