Legal to create a better version of past employer app?

I want to publish an open-source version of an app that I worked on as a side project for the past six years. One of those years, I worked at a small public company that offers a feature of my app as their flagship product.

I'd like to create a wayyyy better implementation of that feature and it is a must for my open-source app.

My feature is implemented in a completely different language, method, and UI. Would I get into any trouble for releasing an open-source version of that feature alonside the main app that I developed?