StringBuilder + link

StringBuilder + link

I have this code
public string DeletedMessage(int id) {
StringBuilder query= new StringBuilder();
query.AppendLine("test");
query.AppendLine("");
query.AppendLine("test - "+"http://test.com/test/"+id);
return query.ToString();
}
And this link comes to as a string and not a link, How can i add link to
StringBuilder line ?