A 5.19ct cushion modified brillant synthetic diamond has been identified by the GIA in Hong Kong. It was not disclosed as a synthetic.
It is a high quality stone of J colour and VS2 clarity. It did not contain any black inclusions which are typically a strong sign of synthetics.
After the examination, the stone was laser inscribed with the words “Laboratory Grown” on the girdle.

The detailed story of how the GIA deduced that this diamond was not genuine is quite interesting. Read more here:
http://www.gia.edu/gems-gemology/winter-2016-labnotes-CVD-synthetic-diamond-over-5-carats-identified