Simplify the following text for a Grade 7 native English-speaking person.
Original: It is not known when Princess Taiping was born , but it is known that she was the youngest of six known children of Emperor Gaozong and his second wife Empress Wu ( later known as Wu Zetian ) .
Simplified: Princess Taiping was a princess of Tang dynasty China . She was the daughter of Emperor Gaozong and Empress Wu Zetian .