Alternator removal

[Iantay16]

Hi all, not very mechanically inclined but I like to have a go when I can, I am in the process of removing the alternator from my Audi 80 se 2 ltr 1995, all was going surprisingly well until I got to the bottom ( bolt???), It is hidden in the plastic belt cover and doesn't seem to be a bolt at all, it's the one you slacken off to adjust the tension, can anyone please advise on how to remove it, thank you in anticipation, Ian.

[WPAWS]

could be an allen key ?