Wikipedia
The Son of Heaven is an imperial title originating from the ancient Han Chinese emperors and subsequently adopted by other East Asian monarchs that was founded on the theoretical principle of the cosmic Mandate of Heaven. The Son of Heaven is a universal emperor who rules tianxia comprising "all under heaven" which translates from the ancient Chinese into English as "ruler of the whole world." The title was interpreted literally only in China and Japan, and the Chinese and Japanese monarchs were referred to as a demigod, deity or " living God" chosen by the cosmic intelligence or entity referred to as the "Heavens" which in ancient Chinese sources usually referred to the universe.
Usage examples of "son of heaven".
But next time he must come in person- I wish to look upon the face of this boy who has sat and chatted with the Son of Heaven.
The bamboo still reigns in China, and the son of heaven bastinades, for the most trivial fault, the Mandarin, who in his turn bastinades the people.
So Methuselah described how a boy had appeared in his son's family who looked much more like a son of heaven than a man.
He is called Agni, son of Heaven and of Earth, or the son of Brahma, or of Kasyapa and of Aditi, or of Angiras, king of the Manes.
He might have been called a provincial, accused of filial impiety, and all but accused of treachery to the Son of Heaven, but he knew his own mind.
The court of Pekin was astonished by an embassy from its former vassal, who, in the tone of the king of nations, exacted the tribute and obedience which he had paid, and who affected to treat the son of heaven as the most contemptible of mankind.