Square Quadrillion® diamonds are the "new" princess-cut diamond. This cut is relatively new and is also known as a Squarillion cut. Quadrillion diamonds exceed the brilliance of standard princess-cut diamonds.

Before 1980, when the cut was developed, square-shaped diamonds were only available in a dull step-cut version. It took two years to perfect the cut, but the result was a square shaped diamond cut to the ideal proportions for the shape and with the brilliance of a round diamond. Prior to the Quadrillion cut, square diamonds displayed much more undesirable light leakage.

The Quadrillion cut diamond consists of 49 facets which progressively narrow towards the girdle and corners, creating a multiple star effect in the center of great brilliancy.