London jeweller Alisa Moussaieff secured the winning bid of HK$49.9 million ($6.4 million) for a 5.16-carat blue diamond at a Sotheby's auction in Hong Kong.

“It’s a bargain and I got it at this price because everyone was asleep,” Moussaieff said in an interview, reported by Bloomberg.

The fancy-vivid, internally flawless gem has a market value of about $1.5 million per carat, according to Moussaieff.

Some experts believe diamond prices will not return to pre-credit crisis levels for at least a decade. However, large, unflawed, colored stones have reached record price levels in the past two years. A 7.03-carat blue diamond was bought by Hong Kong property tycoon Joseph Lau last May in Geneva for 10.5 million Swiss francs ($9.8 million).