The Chalchaj 'qmey, which means a Child of Heaven when translated, are a genetically engineered hybrid species that were created jointly by the Klingon Empire and Romulan Star Empire in the years when the two governments believed an all out war with the Federation would devastate the quadrants. (TOS novel: The Ashes of Eden)
They were among the second generation of genetically engieered Klingon/Romulan hybrids created on the Chal colony. In addition to the qualities inherited from their parent species, the race had the addition of Human organs that were harvested from prisoners obtained by both the empires. Their immune systems were also very advanced and resisted the effects of stasis. (TOS novel: Dark Victory)
The first generation of Chalchaj 'qmey from the Romulan side were actually outcasts, political prisoners and other undesirables. Those that were not exiled to Remus were instead sent to the Chal colony. As such, there is some level of kinship between the Chalchaj 'qmey and the Remans. (TOS novel: Captain's Blood)
The race appeared as humanoids with the distinctive Klingon forehead ridges and the pointed ears that marks their Romulan ancestry.