Company reports unprecedented bidding for white and fancy colours.
Has "several formal and legal evidences" to say he still owns diamond.
Company sees revenue spike at US$65.7m in last six months of 2013.
Customer demand and prices increase in 2013 with 31.2m carats mined.
Diamonds from Letseng mine will be sold at company's February tender.
Reports to use exclusive GIA paper and QR codes from January 1.
Bonhams bags $8.2m for pear-shaped diamond weighing almost 18 carats.