In nested grid not able to take outer grid row index at inner grids events

protected void inner_grid_RowEditing(object sender, GridViewEditEventArgs e)
{
            // Get selected row 
            GridViewRow row = (GridViewRow)(sender as Control).Parent.Parent;
            int index = row.RowIndex;
            // Get Inner grid view
            GridView inner_grid = new GridView();
            inner_grid = outer_grid.Rows[index].FindControl("inner_grid") as GridView;
}