protected void gvwProd_RowCreated(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.Header)
    {
        GridView gvw = (GridView)sender;

        GridViewRow HeaderRow = new GridViewRow(1, 1, DataControlRowType.Header, DataControlRowState.Insert);

        TableCell HeaderCell = new TableCell();
        HeaderCell.Text = "Prod Comments - TS/LID";
        HeaderCell.Style["font-weight"] = "bold";
        HeaderCell.ColumnSpan = 4;
        HeaderCell.Wrap = false;
        HeaderRow.Cells.Add(HeaderCell);

        HeaderCell = new TableCell();
        HeaderCell.Text = "Materials Comments - TS/LD";
        HeaderCell.Style["font-weight"] = "bold";
        HeaderCell.ColumnSpan = 8;
        HeaderCell.Wrap = false;
        HeaderRow.Cells.Add(HeaderCell);

        HeaderCell = new TableCell();
        HeaderCell.Text = "Plant Comments - TS/LID";
        HeaderCell.Style["font-weight"] = "bold";
        HeaderCell.ColumnSpan = 11;
        HeaderCell.Wrap = false;
        HeaderRow.Cells.Add(HeaderCell);

        gvw.Controls[0].Controls.AddAt(1, HeaderRow);
    }
}

((Table)gvw.Controls[0]).Rows.AddAt(1, HeaderRow);