There appear to be a number of *-quel* words formed by [back-formation][1] from *sequel*.

According to [this page][2]:

>  - a *sequel* is a story that takes place later in the same imagined history of a story using many of the same characters and settings
> 
>  - a *prequel* is a story written or published after a certain other story, but whose events take place earlier in the same imagined
> history
> 
>  - a *paraquel* is a story that takes place at the same time as another story with the same or similar characters
> 
>  - an *inquel* is a story that takes place during a gap in another story’s narrative.
> 
>  - a *circumquel* is a story that takes place partly before and partly after another story.
> 
>  - when a story is a prequel to one book, but at the same time a sequel to another, we are reading an *interquel*.

The page cited provides several examples that may help you decide where your situation fits, but what you describe sounds most like a *paraquel*. 

  [1]: https://en.wikipedia.org/wiki/Back-formation
  [2]: https://thestorytellersscroll.blogspot.com/2011/03/what-is-paraquel.html