It's Naomi Watts As Princess Diana
I forgot that this was happening, but this is definitely happening. Naomi Watts is in Croatia shooting the movie Caught in Flight, which IMDB says is only going to focus on the time in Princess Diana's life when she had an affair with heart surgeon Dr. Hasnat Kahn (played by Sayid from Lost). So yeah, unfortunately there won't be a scene in the movie of Princess Diana giving birth to an orb of ginger sunshine and naming him Prince Harry.
These are some of the first pictures of Naomi in full Princess Di drag and I don't know. In some angles, Naomi looks so much like Princess Di that "Candle in the Wind" starts playing in my head and in other angles, she just looks like Naomi Watts in a reworked Leif Garrett wig. Whatever, I'm sure she'll pull it off and if she doesn't, at least she can recycle that wig and wear it to play Tina Brown in a biopic.