Don't buy from Diamond Nexus. I've had my ring less than 3 years and the stone fell out of the setting. The company inspected the ring and told me that it had fallen out because of my lifestyle. They said I could trade-up my ring, which means I send my ring back to them, they then give me a credit for it toward purchasing a more expensive ring, I then pay the difference. They repeatedly claim their jewelry is of heirloom quality. It's not.
Also, please be aware that their stones are NOT lab-grown diamonds. They are man-made stones, like moissanite and cubic zirconia are man-made stones. Don't be fooled by their referring to them as "lab-grown diamond simulants." It sounds like lab-grown diamond, doesn't it? It's all marketing trickery.
Save yourself the heartache, don't purchase from Diamond Nexus.