11 Classes [class]

11.8 Member access control [class.access]

11.8.7 Multiple access [class.paths]

If a declaration can be reached by several paths through a multiple inheritance graph, the access is that of the path that gives most access.
[Example 1: class W { public: void f(); }; class A : private virtual W { }; class B : public virtual W { }; class C : public A, public B { void f() { W::f(); } // OK };
Since W​::​f() is available to C​::​f() along the public path through B, access is allowed.
— end example]