I want my fat son-in-law to stop sitting in my chairs

DEAR ABBY: I have a set of Chippendale-style dining chairs that are more than 100 years old. They are of sentimental value to me because I grew up with them. Recently, at considerable expense, I had them repaired and reupholstered. My husband’s son-in-law, “Isaac,” whom I love very much, weighs between 450 and 500 pounds. When the family is dining, he uses one of the chairs. They are not intended to hold such weight.

My husband and I agree that we should buy a heavy-duty chair that can accommodate Isaac’s weight. However, I don’t know how to convey to Isaac that the new chair is for him without causing offense or hurt feelings. Do you have a suggestion?