Hi,
Please refer below code.
HTML
<div id="dvText" runat="server">
</div>
C#
string text = "Skyfall has good director, and this director is famous";//Get it from Database
string dirctorname = "David";//Get it from Database
string resulText = text.Replace("director", string.Format("<b><span title={0}>{1}<span></b>", dirctorname, "director"));
dvText.InnerHtml = resulText;
screenshot