Displaying “Last Comment By” username

Hello there,

I’ve been playing around with a WordPress theme and want to recreate something I’ve seen on other blogs, but haven’t quite worked out how to do it in WordPress. My current theme displays the following under the contents of each post:

26 Comments | Add Comment

I want to display the username of the last person who commented on a post in addition to the above, e.g:

26 Comments | Last Comment by JimBob123 | Add Comment

Is there a tag that allows me to display this username, or will it require some extra work?