In the 27th year of reign of his father Amenhotep III. Pharaoh Akhenaten was known as Amenhotep IV prior to his 5th year of co-regency.
NEW CHRONOLOGY (ROHL)
Amenhotep III promoted the rise of new cult of sun god worship to Aten. His son Amenhotep IV spread the adoption of the cult by renaming himself Akhenaten.