How to remove a fork from a deleted repository?

I recently removed one of my repositories, but someone has forked it before I deleted it, and the fork is still there. How would I delete the fork as well? I do not want my now deleted repository’s code public.

I don’ think you can.

In any case: Putting something on the internet basically means you give up control of it, code is not different from anything else people don’t want shared.