Business INsider reports Celebrity couple Chris Pratt and Katherine Schwarzenegger announced their engagement in an Instagram post on Monday. In the photo, Schwarzenegger could be seen wearing an engagement ring beset with an enormous diamond. A diamond expert told INSIDER that the diamond weighs at least five carats and estimated its value to be between $350,000-$400,000.Other experts said the value could even be as high as $750,000 if the diamond exceeded five carats.