Are you feeding live, f/t, or p/k?
How else have you tried offering him food and how frequently?
What was his weight in grams before the weight loss and after?
How does he seem weaker?
Do you have any pics of him?
Has anything changed husbandry wise and please describe how you're keeping him and at what temps?

My adult king (4 years old) always slows down in the cooler months for 1-4 months of not eating and then he decides to eat when it gets to Spring-ish, has your guy ever refused food before now?