At its root, it was the Second Prince's palace coup and rebellion that left a deep shadow in the emperor's mind. Any son touching military power made the emperor extremely jittery.
Today, Bai Qingyan suddenly learned that King Liang planned to deceive Dong Tingzhen into marrying him. She deliberately had Bai Jinzhi hint to the Crown Prince that King Liang might be secretly allying with King Xian of Nandu. The Crown Prince might want to create an impression for the emperor that King Liang was trying to marry Dong Tingzhen while entangling himself with Liu Ruofu, who was already betrothed to the Fourth Prince of Daliang.
Given the emperor's suspicious and cautious nature regarding his sons having military power, he would undoubtedly think that King Liang wanted to use the marriage to gain the support of King Xian and Dong Qingyue, who held significant military power.
Then, King Liang's good days would be over.