My Ex is demanding money

My issue is that my ex wife as now after 4 years demanded a rather large sum of money. The history here is that about 16 - 17 years ago we both borrowed a sum (I am not sure of the exact sum of money) from my ex wife's mother for the down payment to an apartment. I then started to pay off the sum each month for about a year then my ex wife's mother said that we did not have to pay the rest of the loan. The rest of the loan was a gift. I unfortunately do not have any paperwork and there was never a written agreement made for anything agreed. My ex wife's mother has passed away so we can no longer seek conformation of the verbal agreement. A few years ago we got divorced and both agreed and signed the bodelning with an attorney which was then submitted with the divorce papers to the court. What is the chances I will be taken to court and made to pay the very large sum of money.