Hmm, the design did look very familiar once I saw the picture. Unfortunately I couldn't find any exact match though.
However, I did find quite some mods which might contain something of interest to you... and if you have to edit one or two to create something closer to what you're looking for for your own personal use:
https://www.nexusmod...vion/mods/48972 - a different piece from Gothic even
The lady has only high quality work and not all of it is revealing/mature, for those not interested in that.
And there's more where I found those.
Haven't found an outfit that's exactly matching this robe, yet, though.