Last seen on an official event (Feb. 3, 2012 at CIFF) in its original form:
The family went to Verbier for a ski holiday in mid-February.
On Princess Mary's trip to Washington, DC on Feb. 27, 2012, her engagement ring had two additional emerald-cut diamonds on either side of the rubies. Sorry, I don't have an HQ photos to post.
These are the best images I could find of the current ring.