'm so happy to see this tv-series. At least I am not the only one who know. Wu Zetian didn't practically become emperor Taizong's wife. I'd say that's why she was in rank 5 concubine for 12 years. She didn't ask for a promotion or anything. She just worked for the Emperor Taizong as a secretary. As a matter of fact she love emperor Taizong like her own father. She did love him and take care of him just like her dad. This is a reason why the Emperor kept her by his side. He considered her like his daughter as well.It might be difficult to believe that Emperor Gaozong was a talented ruler. He really was. Over 30 year within his reign, this can be proved how talented he was. The confusion happened cuz he let empress Wu be there at the parliament instead of him when he got sick. But who know most of government plan that launched. It's all created by emperor.
'After Tang III' - my interpretation - 'Wu will rule' the Tang Dynasty after the death of the 3rd Tang Dynasty Emperor Daozong, the son of 2nd Tang Dynasty Emperor Taizong (the best Emperor of China) who ruled for 23 years from 626AD - 649AD. Wu Mei Niang had married Emperor Taizong at 13 years old. Later on had married her step-son Emperor Daozong and at 26 years old become an Empress in 655AD. Later on the only Female Emperor of China.