Is Yongzheng a usurper or a legitimate heir?

Yongzheng is the successor, and there is no history book saying that he is a usurper.

Yongzheng was the title of Yin Zhen, the fifth emperor of the Qing Dynasty, and Yong Zhengdi was born in 1678. Wu Yashi, the biological mother (namely, Empress Xiao Gongren), was raised by the imperial concubine of Tong Jiashi (namely, Empress Xiao Yiren).

Yin Gui, the 14th son of Emperor Kangxi, is the same mother and brother. He studied under Gu's eight generations, and Xu. On February 20th, A.D. 1722, Kangxi died. Yin Zhen became king at the age of 45. Yin Zhen died on 173518 October at the age of 58.

Extended data:

In the last years of Kangxi, he competed with other princes for the throne of Chu. After the death of his holy father, he succeeded to the throne with the help of Andrew, the thirteenth son of the emperor. It is also said that with the help of Long Keduo, the throne of Yin Gui, the general of Fuyuan, was seized. Whether Yongzheng inherited the throne from Kangxi or tampered with the testamentary edict to seize the throne is a controversial issue, and there is no conclusion yet. But most historians judge that Kangxi's testamentary edict is Manchu, Chinese and Mongolian. According to folk sayings, it has modified Chinese, but Mongolian and Manchu cannot be modified.

Moreover, folklore spread to the Fourteenth Prince and was changed to the Fourth Prince by Long Keduo. However, according to the rules of official document writing in Qing Dynasty, there are no so-called four princes and fourteen princes, but four princes and fourteen princes. Up to now, about10 million Qing dynasty documents in the Forbidden City are no exception. The word Yu was only used as a name in ancient times, and its transmission should be "Yu". From the analysis of writing habits and contents, folklore can basically be regarded as rumors.

Baidu Encyclopedia-Yong Zhengdi