 On the death of his elder brother Colonel Thomas Frederick Mackenzie Humberston in 1783, Francis Mackenzie became the last male heir of the attainted Earls of Seaforth.When he was about twelve years of age, Francis contracted scarlet fever, which incurred the loss of his ability to hear and almost all of his ability to speak.As a consequence, he was known as MacCoinnich Bodhar (Deaf Mackenzie in Gaelic).