Click event of Image button inside gridview is not firing for first time. but firing for second time

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C#

ASP.NET

Can anyone solve this. Click event of Image button inside gridview is not firing for first time. But firing for second time. Below is my code. Thanks in advance.

 protected void Page_Load(object sender, EventArgs e)
 {
   // some code //
 }
 protected void Page_PreRenderComplete(object sender, EventArgs e)
 {
   // some code //
 }
 protected void grid1_RowCommand(object sender, GridViewCommandEventArgs e)
 {
    if (e.CommandName == "Edit")
    {
      // some code //
    }
 }
 protected void grid1_RowEditing(object sender, GridViewEditEventArgs e)
 {
 }

Design :

<asp:GridView ID="grid1" runat="server" AllowSorting="True" CssClass="GridStyle"                                                                              AutoGenerateColumns="False" OnRowCommand="grid1_RowCommand" DataKeyNames="ID" OnRowEditing="grid1_RowEditing" OnRowDeleting="grid1_RowDeleting">
   <Columns>
       <asp:BoundField DataField="ID" HeaderText="ID" ReadOnly="True" SortExpression="ID" Visible="false" />                    
       <asp:BoundField DataField="FirstName" HeaderText="First Name" ReadOnly="True" />
       <asp:BoundField DataField="LastName" HeaderText="Last Name" ReadOnly="True"  />
       <asp:TemplateField HeaderText="Edit">
           <ItemTemplate>
            <asp:ImageButton ID="imgEdit" ImageUrl="~/Images/edit.jpg" ToolTip="Edit Record"                  CommandName="Edit" runat="server" />
           </ItemTemplate>
       </asp:TemplateField>
       <asp:TemplateField HeaderText="Delete">
         <ItemTemplate>
         <asp:ImageButton ID="imgDelete" ImageUrl="~/Images/Delete.gif" ToolTip="Delete Record" CommandName="Delete" runat="server" OnClientClick='return confirm("Are you sure you want to delete this item?");' />
          </ItemTemplate>
       </asp:TemplateField>
    </Columns>
</asp:GridView>