The shortest British monarch (not counting those who ascended as minors) was most likely Queen Victoria, who stood only 5' tall when in her 30s, and would have more than likely been an inch or two shorter towards the end of her life.
All the answers I get say Queen Victoria but the question says king I'm sorry I don't know if minors count or no I have written the question as it is printed, so your guess is as good as mine.
Well, you can't get Queen Victoria as an answer if you google 'King' can you? If you go for monarch you might, but according to you it's king in the question so you don't want " Vickie",surely? I would suggest Charles 1.