佛祖歷代通載 21.60

21.60

（乙丑）　宋改咸淳元年。度宗即位。初名孟[啟-口+山]。福王與芮之子。理宗之猶子也。理宗子多而不育。鞠孟[啟-口+山]於宮中。改名孜。又改名祺。立為皇子。封忠王。已而建儲。改名璿。

(Yichou) The Song changed the era name to the first year of Xianchun. Emperor Duzong ascended the throne. His original name was Mengqi, the son of Prince of Fu Yurui and the nephew of Emperor Lizong. Lizong had many sons who did not survive, so he raised Mengqi in the palace, changing his name to Zi, and then changing it again to Qi, creating him as an imperial son and enfeoffing him as Prince of Zhong. Soon after, he was established as the crown prince and his name was changed to Xuan.