Why did he die in the ending of "Prince Concubine's Promotion"?

At the end of "Prince Concubine's Promotion", the protagonist dies due to being assassinated by an assassin. This plot takes place in the thirty-fifth episode. The plot at that time was:

Qi Sheng asked Zhang Pengpeng if he was willing to be his wife now, and Zhang Pengpeng sweetly said the words "I do." From then on, the two lived in seclusion and lived like a couple of gods and immortals. Zhang Pengpeng was assassinated and died. Before she died, she told Qi Sheng to live on, which made Qi Sheng very sad. Many assassins surrounded Qi Sheng and killed him with random knives. The falling petals buried the bodies of the lovers.

Extended information:

The play is adapted from the novel of the same name originally written by Xian Cheng. In 2012, Gan Wei, who was interested in the theme of men wearing women, women's bodies and men's hearts, bought the copyright and The project was started in 2014; the screenwriting team has been communicating with the author at the beginning of creation. On the basis of retaining the main structure of the story, the plot, design, plot and other aspects have been adapted to be more conducive to film and television presentation. At the same time, Based on market research, we also adjusted and accelerated the pace of the plot. In fact, only 10% to 15% of the novel was filmed.

The director decided to cooperate with Gan Wei after being recommended by the script writer. Before filming, he had not read the novel because of the screenwriter's suggestion. Since the broadcast schedule has been set, preparations for the play were in a hurry, and props and other items were not available before filming. Failure to fully prepare;

On August 1, 2015, the drama started shooting at Xiangshan Film and Television City, with a 70-day shooting period, mainly in Zhao Dun Mansion, Gongsun Mansion, Zhuang Ji Mansion, Xiangyang City and the studio View inside. On January 25, 2016, the producers announced that they were filming the third ending of the show.