C++: struct automatically compiled in namespace - c++

Question

I'm using the d3dx9.h header to be able to use many of the Direct3D functions and datatypes. One of which is 'D3DXVECTOR3'. I have stumbled upon a weird issue of which I can't find the cause:
I have two files, Link.h and Link.cpp. Link is a static class. In my Link.cpp and Link.h I have included the d3dx9.h file as follows:
#ifndef D3DX9_INCLUDED
#define D3DX9_INCLUDED
#include <d3dx9.h> // Direct3D 9
#endif
In Link.cpp I have created a function to get a D3DXVECTOR3 variable:
#pragma once
#ifndef D3DX9_INCLUDED
#define D3DX9_INCLUDED
#include <d3dx9.h> // Direct3D 9
#endif
namespace Core
{
static class Link
{
private:
public:
static struct D3DXVECTOR3 getVector()
};
}
My Link.h script makes this public:
static struct D3DXVECTOR3 getVector();
Now, when I call this function from outside this class it keeps giving me the error
error C2027: use of undefined type 'Core::D3DXVECTOR3'
This is how I call the getVector function:
Core::Link::getVector();
I get the error even though D3DXVECTOR3 is not a member of 'Core'. I have included d3dx9.h the same way outside this class.
I have tried exactly the same with standard datatypes such as a bool, worked like a charm. Why does getVector return a D3DXVECTOR3 as a child of Core?