[TYPO3] $_GET in mailform

[Lee M. Childress]

I'm sure this has asked before and honestly, I have searched, but didn't find it.
 
I would like to have a link: mydomain.com/index.php?id=99&aid=description where id is the page where my mailform is and I would like to include $_GET['aid'] in a hidden field of the mailform. Is there a way to include a $_GET variable as the value of a hidden field?
 
Thanks in advance for your help. You all are always awesome!