Does Colossus Slayer work with an Attack of Opportunity?

I have my turn hit my opponent and get to use Colossus Slayer then on their turn they turn around and run away giving me an Attack of Opportunity, as that is on their turn does that mean I can use Colossus Slayer twice, once on my turn and once on their turn?

Colossus Slayer states damage is only once per turn. As Colossus Slayer does not explicitly state your turn I can see some room for confusion or debate over this