question: Who is Li Zhong's paternal grandmother?
context: Title: Emperor Gaozong of Tang
  Passage: Emperor Gaozong of Tang (21 July 628 – 27 December 683), personal name Li Zhi, was the third emperor of the Tang dynasty in China, ruling from 649 to 683 (although after January 665 power and governance was primarily in the hands of his powerful second wife Empress Wu, later known as Wu Zetian). Emperor Gaozong was the son of Emperor Taizong and Empress Zhangsun. Emperor Gaozong was aided in his rule by Empress Wu during the later years of his reign after a series of strokes left him incapacitated. Emperor Gaozong delegated all matters of state to his Strong wife and after he died in 683, power fell completely into the hands of Empress Wu, who subsequently became the only Empress regnant in Chinese history. After his death, he was interred at the Qianling Mausoleum along with Wu Zetian. Historians have generally viewed Emperor Gaozong as a weak ruler, inattentive to the business of the state and leaving such business to his powerful wife Empress Wu. During the first part of his reign, Tang territorial gains, which started with his father Emperor Taizong, continued, including the conquest of Baekje, Goguryeo, and the Western Turkic Khaganate, but throughout the 670s, much of those gains were lost to the Tibetan Empire, Silla, Khitan, and Balhae. Further, territory previously conquered that belonged to both the Göktürks and the Western Turkic Khaganate were subjected to repeated rebellions.
  Title: Li Zhong
  Passage: Li Zhong (李忠) (643 – January 6, 665), courtesy name Zhengben (正本), formally Prince of Yan (燕王), was a crown prince of the Chinese dynasty Tang Dynasty. He was the oldest son of Emperor Gaozong (Li Zhi) and was created crown prince in 652 even though he was not the son of his then-wife Empress Wang. After Empress Wang was displaced by Empress Wu (later known as Wu Zetian) in 655, however, Li Zhong was caught in Empress Wu's crosshairs and was forced to yield the crown prince position to his younger brother Li Hong, born of Empress Wu, in 656. He was later further reduced to commoner rank and put under house arrest, and when the chancellor Shangguan Yi failed in his attempt to persuade Emperor Gaozong to depose Empress Wu in 664 and was executed, Empress Wu took the opportunity to accuse Li Zhong of being complicit in Shangguan's plans. Around the new year 665, Emperor Gaozong ordered Li Zhong to commit suicide. He was posthumously honored an imperial prince, but not a crown prince, during the second reign of his brother Emperor Zhongzong.
answer: Empress Zhangsun
citations: Emperor Gaozong of Tang Li Zhong