Datagridview - How to update programatically a hidden column in C# winforms.

Question

Datagridview1 contains 3 columns.
  1st  :  ID
  2nd   : Name
  3rd   : ModifiedDate

third column is hiden

I would like to update automatically the hidden column (Modified Date) each time I modify the Second column value (Name)

Something is wrong with the next :

  dataGridView1.CurrentRow.Cells(2).Value = dateTime.Now;
  MyEntities.SaveChanges();

Thank you in advance.