How to ensure that future Implementations of an Interface will also extend a particular Class

I have an abstract class and two final classes that extend it.

The abstract class is also an implementation of an interface.

Now I have to remove one of the two child classes and add an interface so that people can still come in with their own implementations.

But I need to ensure that whoever implements the new interface is going to extend the existing abstract class. It is required because otherwise it won't be functioning.

Is there a way to achieve that, or I can only document an implementation requirement?