Why does this CRTP-based clone pattern correctly return a Derived pointer without each subclass rewriting clone()?

struct Base { virtual Base* clone() const = 0; virtual ~Base() = default; }; template <class D> struct Cloneable : Base { Base* clone() const override { return new D(static_cast<const D&>(*this)); } }; struct Foo : Cloneable<Foo> { int x; };