c# - duplicate Combobox is adding in cells in datagridview -

i using dynamic combo box in datatgridview , populating correctly. when tried add new row datagridview,by clicking button add new row,this combo box repeating in cells. if click once , 1 combo box added in cell1,second click add 1 more row,two combo box added in cells. how can add new row in datagridview without repeating combo box in cells? code follows:

 private void btnrmadd_click(object sender, eventargs e)         {             //add new row             dgitemgroup.rows.add();             fninsertcolumnscombo();         }   private void fninsertcolumnscombo()         {             datagridviewcomboboxcolumn combo1 = new datagridviewcomboboxcolumn();             combo1.name = "groupname";             combo1.headertext = "groupname";             string sqlstr = "select groupid,groupname tblitemgroup ";             sqlcommand cmd = new sqlcommand(sqlstr, con);             sqldataadapter da = new sqldataadapter(cmd);             datatable dt = new datatable();             da.fill(dt);             combo1.datasource = dt;             combo1.displaymember = "groupname";             combo1.valuemember = "groupid";             combo1.autocomplete = true;             combo1.flatstyle = flatstyle.flat;             dgitemgroup.columns.insert(0, combo1);             dgitemgroup.columns[0].width = 250;         } 

in method fninsertcolumnscombo, adding new column grid each time add new row. method called each time add new row. maybe want add column in "init" phase , populate data after adding new row.