Morgana & Igraine, Season Three

[majorshipper]

*SEASON 3 SPOILERS FOR MERLIN* 
I SAY AGAIN! DO NOT READ IF YOU DON'T WANT TO SEE SPOILER-ISH PIC AND SPECULATION! (With full S2 spoilers as well)
Okay now that that's outta the way, and you assumedly clicked on the cut, let's begin. This was kinda discussed on camelot_love when the on-location pictures were first released, but never to any kind of detail (at least not while I was there). But this fascinates me to no end. Really. Check out the pictures. The first one is from season two (credit for picture goes to Merlin Wiki), the woman being Igraine, Arthur's deceased mother, who was 'conjured' by Morgause. It's unknown if she's actually his mother or not, but judging by what she said, it is possible. The second picture (credit for posting goes to yavannauk), is of Katie McGrath from on-location in Pierrefonds, France. Notice anything similar? They're obviously wearing the SAME dress! If you recall, last season (S2), Morgana disappeared with Morgause after being poisoned by Merlin. Obviously she survived, and has returned to Camelot. Now, the biggest question is...why is she wearing Ygraine's dress? Is it a huge plot point or just a lack of costumes? Has Morgause sent her back in Ygraine's dress for a reason? How long will it take Merlin and Arthur to notice? (Surely they're not that stupid to not notice, right?) Anyway. Anyone want to start speculating on the matter?