Public Overrides Sub InitializeEditingControl(ByVal rowIndex As Integer, _
    ByVal initialFormattedValue As Object, _
    ByVal dataGridViewCellStyle As DataGridViewCellStyle)

    ' Set the value of the editing control to the current cell value.
    MyBase.InitializeEditingControl(rowIndex, initialFormattedValue, _
        dataGridViewCellStyle)

    Dim ctl As CalendarEditingControl = _
        CType(DataGridView.EditingControl, CalendarEditingControl)
    ctl.Value = CType(Me.Value, DateTime)

End Sub

public override void InitializeEditingControl(int rowIndex, object 
    initialFormattedValue, DataGridViewCellStyle dataGridViewCellStyle)
{
    // Set the value of the editing control to the current cell value.
    base.InitializeEditingControl(rowIndex, initialFormattedValue, 
        dataGridViewCellStyle);
    CalendarEditingControl ctl = 
        DataGridView.EditingControl as CalendarEditingControl;
    ctl.Value = (DateTime)this.Value;
}