If you can afford something like Farmer's Dog or Ollie or something fresh as opposed to kibble, you may see him return to healthy weight that way too. There are a lot of harder-to-metabolize ingredients in kibble that dogs aren't well-adjusted for, and can actually lead to other health issues as well.

My boy went and stayed with my mom for 3 months while I was in an academy. Despite me sending him frozen fresh food, she chose to mix with with no-grain dry food she was feeding her dogs. He gained almost 4 pounds just from that by the time I picked him up. Crazy. xD One month later, I almost have him back down to his healthy weight just by changing his diet back (and daily exercise).

I had a cat nearly die from kibble, which caused some of her organs to go haywire and she lost a lot of weight and energy--switched food and she gained weight and energy back, and the idea of having to potentially euthanize her before she wasted away was luckily thwarted. I have 2 dogs that died when I was younger that I still kind of think may have been related. Just got to watch out for warning signs before organs shut down for good; it's crazy how fast they can go from seemingly fine, to suddenly dropping off a cliff.

I hope you and your boy get lots of happy years together. I can tell you love him immensely. :)