Sir Robert Jermyn was a noted anthropologist who explored Africa, and was the great-grandfather of Arthur Jermyn. He married a daughter of the seventh Viscount Brightholme in 1815 and had three children including his second son Nevil. The youngest and eldest are unnamed and were never publicly seen due to physical and mental deformities. (HPL: "Facts Concerning the Late Arthur Jermyn and His Family")
When an explorer named Samuel Seaton visited Robert at his home in 1852 with a manuscript of notes collected in Africa, Robert discovered to his horror that there was a simian strain in his own family originating from a union between his grandfather Wade Jermyn and a female member of a race of African white apes. The unhinged Robert murdered Seaton along with his own three children, but his two year old grandson Alfred survived. (HPL: "Facts Concerning the Late Arthur Jermyn and His Family")
During the second year of his confinement in an asylum, Robert died of apoplexy after repeated attempts at suicide. (HPL: "Facts Concerning the Late Arthur Jermyn and His Family")