There is a good chance you can void the note. It's not merely that they gave him a gift letter, though that certainly helps; that is evidence that when made, the money was a gift, not a loan. It's also that they did not get him to sign the promissory note until months after they had already given him the money. If he already had the money, he was not receiving anything for signing the promisory note. If he did not get anything to sign it, he did not receive "consideration" for his agreement to pay; and since a binding contract (which is what a promissory note essentially is) requires consideration, without him getting anything new in exchange for his promise to pay, that promise is not binding. IF he had signed the note, even after first getting a gift letter, *before* receiving the money, so that he only got the money because he signed, the money would be a loan; but you can't retroactively convert a gift into a loan after the recipient already received the money.