// in Form1
private void button1_Click(object sender, EventArgs e) {
    Form2 form2 = new Form2();
    form2.ShowDialog();
    Debug.WriteLine ("INFO: LastLineNumber: " + form2.LastLineNumber.ToString( _
      ));
    form2.Dispose(); form2 = null;
}
 
// in Form2
public int LastLineNumber {
    get {
        return this.dataGridView1.CurrentRow.Index;
    }
}