Html Editor inside ASP.Net Gridview

I have Gridview and I need to add HTML EDITOR to it such as Ajax Editor.  The Editor needs to replace the textBox that displays when I click on the Edit Gridview.  
The gridview has Edit, Delete, Select control.


I have used the below code to re size the Textbox that displays when I click on Edit, but I am unable to replace the TextBox with the Html Editor control.

Any idea to make it work?

Thank you!

 if ((e.Row.RowState & DataControlRowState.Edit) > 0)
            {
                // Comments
                AjaxControlToolkit.HTMLEditor.Editor comments =    (AjaxControlToolkit.HTMLEditor.Editor)e.Row.Cells[7].Controls[0];
                //comments.TextMode = AjaxControlToolkit.HTMLEditor.Editor.MultiLine;
                //comments.Height = 100;
                //comments.Width = 400;


                // Comments1
                TextBox comments1 = (TextBox)e.Row.Cells[8].Controls[0];
                comments1.TextMode = TextBoxMode.MultiLine;
                comments1.Height = 100;
                comments1.Width = 400;


                // Comments2
                TextBox comments2 = (TextBox)e.Row.Cells[9].Controls[0];
                comments2.TextMode = TextBoxMode.MultiLine;
                comments2.Height = 100;
                comments2.Width = 400;


            }
        }