What kind of bling sets a groom-to-be back $2 million?

RadarOnline.com spoke to jewelry expert Michael O’Connor, to get the lowdown on why Kim Kardashian’s 20.5-carat stunner is worth more than a mansion.

PHOTOS: Celebrity Engagement Rings!

“Kim’s ring is a MAJOR rock,” O’Connor gushed to Radar about the bootylicious star’s Lorraine Schwartz stunner.  “We have seen a number of celebrities get engaged over the past few years, but nobody has had a diamond of this size and quality!”

So what is so special about Kim’s ring and how do we know it is top quality?