Detect the last cell of AdvStringGrid

I'd like to know the way to detect the last cell to move focus to the next control.
The last cell is the cell except for ReadOnly cell when Navigation.AdvanceSkipReadOnlyCells := true;

If cell B3 is selection and Enter key is pressed, 
I do not understand to move focus to a button on following sample application.

I use AdvStringGrid ver and Delphi XE8.

Sample application
put a TAdvStringGrid and TButton on TForm1, and OnCreate event is below.

procedure TForm1.FormCreate(Sender: TObject);
var i:integer;
    AdvStringGrid1.ColCount := 4;
    AdvStringGrid1.RowCount := 4;

    for i := 1 to AdvStringGrid1.ColCount-1 do begin
        AdvStringGrid1.Cells[i, 0] := Char(ord('A')+i-1);
    for i := 1 to AdvStringGrid1.RowCount-1 do begin
        AdvStringGrid1.Cells[0, i] := Char(ord('1')+i-1);

    AdvStringGrid1.Options := AdvStringGrid1.Options + [goEditing];
    AdvStringGrid1.Navigation.AdvanceOnEnter           := true;
    AdvStringGrid1.Navigation.AdvanceOnEnterLoop       := false;
    AdvStringGrid1.Navigation.AdvanceSkipReadOnlyCells := true;

    AdvStringGrid1.ReadOnly[3, 3] := true;
    AdvStringGrid1.Cells[3, 3] := 'RO';

The Enter key will not move the focus to the next control.The enter key moves focus within the grid only.

There is currently not a built-in function to detect the last not readonly cell of the grid. You'd need to add the code to detect this at application level.