Is Zakat due on a benevolent loan (Qard Hasan) that was repaid after several years, and is it due for one year or for all the past years?

If the debtor is insolvent or procrastinates, there is no zakat on the loaned money until it is recovered, and then zakat is paid for one year. However, if the debtor is solvent and able to pay whenever you wish, then this money is considered to be like a trust, and zakat must be paid on it every year.