Link rollover thumbnail tooltips

Greetings there,

I got a request to help to create a new feature for a WP site.
There’s a page with loads of links listed, all of them point to 1-1 subpages.
The goal would be: when the client rolls over the links, the target page’s thumbnail should appear as a tooltip.

Would you have an idea/plugin/whatever how to manage this out?
Thank you in advance.