My fiancé proposed with a 1.5ct round G-VS1 in a platinum solitaire. It was stunning. He spent months researching and I was genuinely moved. But three weeks later I started noticing something under certain lighting. A milky, haziness. Not in every light — but in diffuse daylight through a window, the stone looked flat. Dead. I brought it to a different jeweler for a casual inspection. She put it under a UV light without me asking. Strong blue fluorescence. Medium-strong, actually. The stone was never disclosed as having fluorescence when purchased. It was not on the original receipt. The online listing my fiancé used said "None" for fluorescence. But this stone was clearly strong blue under UV. We contacted the retailer. They apologised and confirmed it was a listing error. They offered a $200 credit. We returned the ring on day 27 of a 30-day return window. Here is what we learned and what we bought instead: • Always filter for None or Faint fluorescence on round brilliants — Strong blue can make a D-H color stone look oily in diffuse natural light. • The listing error was not malicious but it cost us a month of uncertainty about a purchase that is supposed to feel perfect. • We bought a GIA 1.5ct G-VS1, fluorescence: None, from a different retailer. $6,420. The stone is brilliant in every light condition. If something looks off about your diamond in window light: trust your eye. That is the most honest light your stone will ever be in.