How to get my grandfather to eat?

My grandfather has been quite ill recently, he was in hospital but it was very stressful for him and it has seemed to of made him worse, he wont eat anything and if he does its wierd things like jelly. My nan will make him a lovely tasty stew type soup and he will just have a spoonful, he always used to love stews and roast dinners etc, all he will eat is his bowl of porridge in the morning. He isnt getting up just sleeping on the chair all day in a blanket. How can we make him eat things? Because not eating is making him more weak i think. Also i said what ever you want ill get it for you and he asked for a gl of white wine, he never drinks, especially wine... only beer at christmas. Any advice on helping him eat or what we can give him instead of food will be a great help. Many thanks!