The inner inner class implicitly has a reference to an instance of the inner and outer class.
Also, the inner inner class [default] constructor needs to call the inner class [default] constructor, as its superclass constructor.
Somehow, in a way that I haven't exactly worked out, the compiler needs to access the instance of the inner class before the inner class constructor has been called, as the superclass constructor.
To be honest, I don't think there is a huge amount to be gained by deep analysis of what is going on here (which is why I haven't bothered!). I don't believe there would ever be a good reason to have an inner class that extends its enclosing class. So just Don't Do That Then.
Betty Rubble? Well, I would go with Betty... but I'd be thinking of Wilma.