I think Nikko Hetch is also a good candidate, but the information given on him is so scant (perhaps his background was left out because of space considerations ala the Dread Possibilities?) that I can't say for sure. All that we have to go on is S's quote "Little about Hetch is known, but much is whispered."
True, he does hold a similar role to the Jongleur and Vigo Drakov - serving in close relation to the most powerful person in their respective domains. But we have no physical description (and thus no strange deformities, etc.) to group him in with the GC's other children.
If this is all the information we have to go on, the final candidate will probably be the hardest to find. It could easily be just a miniscule reference (just a name or a description) that is easily passed over.
The authors sure aren't making this easy!
