My guess: a new "super-cuvee" from the vines around the terraces referred to in this description of Quinta dos Malvedos on TheVintagePortSite?
here, TheVintagePortsite wrote:
The house at Malvedos has one of the finest locations of all Douro quintas, with a breath-taking view of the Douro from the tranquility of the veranda. Just to the east of the house are the famous Port Arthur stone walled terraces, so called as their shape was reminiscent of a heavily fortified city of that name which was in the news in the years just after the quinta was acquired. They are among the most striking and best preserved in the Douro, with beautiful integral stairways; superb examples of the stone mason's art.
Edit: also a reference here
to the "Port Arthur" vineyard producing some of the best TN at the Quinta, although it seems like a single varietal block so not sure my guess is correct...BUT reference here
to the separate vinification of 2010 "Port Arthur" grapes with "parcel 37", so perhaps 2011 was the next iteration of this experiment?