Complex sentence: Finally, Theophanes briefly mentions another Gregoras as a brother of Heraclius the Younger on the occasion of the former's the death at Heliopolis (modern Baalbek) c.652/653.
Split into simpler sentences: Finally, Theophanes briefly mentions another Gregoras as a brother of Heraclius the Younger. The occasion of the reference is the death of this Gregoras in Heliopolis (modern Baalbek) c.652/653.