Can not return a TShared memberVariable

In my heade file, I defined:
TSharedPtr GetCanvasWidget() const;
TSharedPtr MySketchpad;
and in Source:
TSharedPtr USketchpad::GetCanvasWidget() const
{
return MySketchpad;
}

When compile, compiler says cant not convert from const TSharedPtr to TSharedPtr

Did I make some thing wrong?