GridView Hide Column by code

I want to hide ID column in my GridView, I knew the code

GridView1.Columns[0].Visible = false;

but the surprise was that my count property for my GridView columns is 0 !!! while I can see data in the GridView, so any ideas?

Thank you,

Update:

here is the complete code for the method which populate the GridView

public DataSet GetAllPatients()
{
    SqlConnection connection = new SqlConnection(this.ConnectionString);

    String sql = "SELECT [ID],[Name],[Age],[Phone],[MedicalHistory],[Medication],[Diagnoses] FROM [dbo].[AwadyClinc_PatientTbl]order by ID desc";

    SqlCommand command = new SqlCommand(sql, connection);

    SqlDataAdapter da = new SqlDataAdapter(command);

    DataSet ds = new DataSet();

    da.Fill(ds);

    return ds;

}