First---I would get rid of the CAT!!

Hey, now. Let's not blame the cat. And he/she is probably not stupid! Has your cat never liked to lay on your items of clothing or quilting projects before? Is this a surprise to you that he/she is doing so now? I'm very sorry for the hole in your newly finished quilt. You must feel awful about having left it out where your cat could lay on it. In circumstances like this I will always advocate for the animal...in this case your wonderful family pet. Anyone else out there feel the same?

You can refer to it as the "Black Hole" little humor

I'm with bakermom, tuck a matching piece of fabric into the hole and patch from underneath. You can use several methods for this but it holds up well and way less obvious.

I agree. Fusing would work very well. You could even machine stitch it after fusing with a plain, or decorative stitch. Your son will love it. Good luck. GiGi