Cem Fel was a Human male and one of the sons of General Baron Soontir Fel and Syal Antilles Fel. Raised as a shadow child first on Nirauan and then on Csilla, Fel was kept secret from all those outside the family until 28 ABY, when his name was leaked to a visiting group of Galactic Alliance Jedi, information which made its way back to Aristocra Chaf'orm'bintrano of the Chiss in 35 ABY.
Fel's parents, Soontir and Syal Antilles Fel
The Human male Cem Fel was the child of General Baron Soontir Fel and Syal Antilles Fel, highly-placed Imperials who joined the Empire of the Hand in 5 ABY. Born on the planet Csilla and raised on Nirauan, Fel's existence was kept secret. He was a shadow child, a custom of the Chiss among whom the Fels lived; in fact, his name, Cem, was of Chiss origin. As a shadow child, Fel was kept completely unknown to the public, so that if ever the family were destroyed by enemies, Cem could keep the Fel line alive. His brothers Chak, Davin, and Jagged all went into the Empire of the Hand's military, as did his sister, Cherith. All of those except Jagged were lost in combat relatively early in Fel's life. His sister Wynssa, however, remained at home with him. While he did not appear in public, Fel was taught to pilot and frequently took out the family yacht Starflare, which annoyed the eager-to-pilot Wynssa.
When the Empire of the Hand ceased to exist and the Fels joined the Chiss Ascendancy, Fel returned to Csilla and settled there with his family, where he remained a secret. In 28 ABY, however, his existence was outed to the visiting Jacen Solo by Wynssa. This information did not make it back to the Chiss until 35 ABY, when Solo's uncle and aunt Luke and Mara Jade Skywalker dropped his name in conversation with Aristocra Chaf'orm'bintrano of the Chiss, who quickly realized that Fel was a shadow child and promised to keep his existence secret. He speculated that the namedrop by Wynssa had possibly been part of a plot by Soontir.
In 36 ABY, the Fels were dishonored and diminished in power by the actions of the Jedi Lowbacca, taken after Jagged granted his parole as an officer of the Chiss Expansionary Defense Force; at the same time, Jagged was himself lost to a crash on Tenupe. While Jagged was recovered two years later, he was exiled, never to be able to return. It was only in 40 ABY, with the death of the Chiss enemy Alema Rar at Jagged's hands, that the family's honor was restored.
Cem Fel has only been mentioned by other characters, first in The New Jedi Order: Force Heretic II: Refugee and then in Dark Nest I: The Joiner King; he has never appeared as a character himself.
The New Jedi Order: Dark Tide II: Ruin, published in 2000, and The New Jedi Order: Dark Journey, published in 2002, established five Fel siblings—Jagged, his older deceased brother Davin, his younger deceased sister Cherith, and two other unnamed children. Force Heretic II: Refugee, published in 2003, filled in the missing two as Cem and Wynssa. All five children had been named when Chak Fel appeared in Survivor's Quest in 2004. This information was retconned in Dark Nest I: The Joiner King, which established that Cem had been a shadow child known to none outside the family; all references to five Fel children were therefore misinformation and included Chak, Davin, Jagged, Cherith, and Wynssa. The Complete Star Wars Encyclopedia, published in 2008, confirmed what had only been expressed as characters' belief by explicitly establishing him as Cem Fel, a shadow child of the Fel family.
The Complete Star Wars Encyclopedia also stated that Fel was born on Csilla. As his family did not join the Chiss Ascendancy and move to Csilla until shortly before he was old enough to pilot yachts, Fel must have been born on the world before his family took up residence there.