How do I handle a back-button press in a (DelphiXE 6) Android app?

Question

How can I make my Android app react to the back-button from Delphi XE6?

    uses
  FMX.Platform, FMX.VirtualKeyboard;

procedure TForm1.FormKeyUp(Sender: TObject; var Key: Word; var KeyChar: Char; Shift: TShiftState);
begin
  if Key = vkHardwareBack then
  begin
     // Back button pressed...
        Key := 0;
  end;
end;

The code above does not work