Make a custom permalink for a specific category

I would like to make 1 post and check off 2 categories, say cat1 and cat2.

I want cat1 to spit out my post like this : site.com/past-name
Then cat2 to spit out the same post like this : site.com/cat2/post-name

For example, if I enter the URL in address bar, site.com/past-name AND site.com/cat2/post-name, the same post would come up, the only different would be between the 2 is the URL.

Is it possible to write a custom permalink structure for a specific category?

I don’t want to use plugins.