One Close statement closes both forms??

Hello,

        Basically here is the pseudo code.

MainForm
        PressMenuItem4
                Form2 F2 = new Form2();
                F2.ShowDialog

Form2
        OpenExelFile
        ProcessRecords
        If (Duprecordfound){
                ShowDupRecordForm SDRF = new
ShowDupRecordForm(PassExeclRecords);
                SDRF.ShowDialog();
                X = SDRF.RecordNumber;
        }

ShowDupRecordForm
        ListOFDupRecords.Item.Add(LoadListwithDupRecords);

        ListSelectChangeIndex()
        {
                Recordnumber = ListofDupRecordsList.SelectedIndex;
                This.Close();
        }
The This.Close command closes the ShowDupRecordForm and Form2 shouldn't it
only close ShowDupRecordForm? And if not how does one do this?