put someone out of their misery

verb3

1. •
   (informal) To submit a suffering person or an animal to euthanasia.
2. •
   (informal, figurative) To end or destroy something for the good of the individuals involved in it.
3. •
   (informal) To relieve somebody's anxiety by supplying information that they wanted to know.

   • Well, I'll put you out of your misery: the amount we won on the lottery was only ten dollars.