Data from another column in GetDisplayText

I try to keep all needed data in my TadvColumnGrid, some invisible data in hidden columns.
Sometimes I need to display some of the hidden data in another column.
Following code leads to a Stack Overflow message.

procedure TFrame_mainGrid.mainGridGetDisplText(Sender: TObject; ACol,
                                                                                   ARow: Integer; var Value: string);
    DatumStr : string;
    if (aCol=clmTitel) then begin
        DatumStr := mainGrid.Cells[clmCreateD,aRow];
        Value := Value +': '+ DatumStr;

Debugger shows, that it endlessly executes the line with DatumStr :=

Is it basically not possible to use data from another column?
Or what is necessary to make it work?

grid.Cells[] will call itself OnGetDisplText, so you can indeed cause an endless loop by this.

If you have data actually stored in the cell and want to access it, please use

DatumStr := mainGrid.GridCells[clmCreateD,aRow];