I say it again since no one listened to me. Fresh grapefruit - probably in secondary. Not sure, but if you have ever had Citrus Ninja - http://westbrookbrewing.com/beers/all/collaborations/citrus-ninja-exchange/ - you will see how well hops and grapefruit pair. You may try contacting the brewery and see if they add the grapefruit to secondary or what.Shorts had grapefruit in their Hopstache IPA. It worked for me.
It is a very good beer.