What is the correct type hint for class factory with multiple inheritance?

What is the correct return type of the following function?

import typing

T = typing.TypeVar['T']
U = typing.TypeVar['U']


def class_factory(class_T: typing.Type[T], class_U: typing.Type[U]) -> ???:
    return type(class_T.__name__ + '_x_' + class_U.__name__,
                (class_T, class_U), {})

Background: I am trying to convert a normal python class T to Subject class (Subject as in the observer pattern). My idea is to create class SubjectT inheriting from both T and Subject:

import typing
T = typing.TypeVar('T')

def create_subject(class_T: typing.Type[T]) -> ???:
    class result_class(Subject, class_T):
        def __setattr__(self, name, value):
            super().__setattr__(name, value)
            self.notify()   # notify observers of all changes
    return result_class  

This works, but my IDE does not offer any code auto-completion for result_class.