According to the AFL website and the Age's report on the final day, Hawthorn traded in Carlton's future second. That then allowed us to trade away our own future second which we did to GC.
I have read and heard conflicting reports about this mind you so I'm not 100% on what actually happened. I'm pretty sure we hold someone's 2017 second rounder, though, and most importantly JOM.
It's odd as I can't find the official rules about future trading (link anyone who can?) but nothing I find mentions anything about being able to trade out a pick from a round if you have another pick.
And while everything I read says we gave up our 2nd rounder, the screenshot AFL.com put up says (ontraded) after the future second round pick.
Oh well, I suppose it's only 1 spot difference when we beat GWS in the GF.