As she had no son of her own , she adopted Tian Ji'an as her son .
After Tian Xu assassinated Tian Yue and succeeded him in 784 , Emperor Dezong gave Tian Xu his sister Princess Jiacheng in marriage in 785 .
As sister had no son of sister 's own , sister adopted Tian Ji'an as her son .
After Tian Xu assassinated Tian Yue and succeeded him in 784 , Emperor Dezong gave Tian Xu his sister Princess Jiacheng in marriage in 785 .