Previous Parent Page?

I’ve created a custom menu in my wordpress website that detects what the current page’s parent page is and from there it determines which menu shows up on the page.

The challenge of this is that when you go to the blog articles on my site there is no parent page, so my menu system is thrown off.

Is there any way to determine the previous page’s parent page?

Here’s an example:

https://mysite.com/parent-page/about-us (Uses the menu for ‘parent-page’)

https://mysite.com/blog/ (Has no parent page and menu system is thrown off)

Any suggestions? Perhaps I can base my menus on something besides the parent page, but I’m not sure what…

-foo