(IDEX Online) - Christie's say a 45.46-ct round brilliant diamond is the highest value gem ever to be offered in an online-only auction.The Flawless Star (pictured), a D/IF Type IIa stone, carries at estimate of $4m to $6m and is being sold without reserve.The record high price actually paid for a diamond in an online-only sale was set in June 2020 when a 28.86-carat, D-color, emerald-cut diamond was sold for $2.11m by Christie's.Last August a 24.45-carat, internally flawless, heart-shaped diamond, narrowly missed the record when it sold for $2.01m, also at Christie's.The Flawless Star leads an online sale of 238 lots which closes on 7 April. More than half have no reserve.Among other highlights are designs by renowned jewelry houses including Buccellati, Bulgari, Cartier, Graff, Harry Winston, JAR, Oscar Heyman & Brothers, Seaman Schepps, Tiffany & Co., Van Cleef & Arpels, and Verdura.