Insert workflow variable with HTML in an email body.

I have a workflow variable that contains HTML markup. 

I want to insert this HTML into an email (Send Notification action).
But the HTML gets formatted and displayed literally in the email instead of being part of the email HTML layout.

--W

PS :  The HTML in the variable is dynamically generated by an other system and contains various links. I got the HTML by using a "Call Webservice" action. I can not recreate these complex links in our Nintex / SharePoint context.