Kim Yushin
One of the theories about it was that: During the time that Queen Seondeok's health was getting worse, the talk about her successor became an issue especially because Queen Seondeok refused to name her successor (out of fear of being manipulated). Bidam, who was a Sangdaedeung at that time and was people's favorite, has the strongest chance to become the next ruler. One night, Kim Yushin started a secret coup inside the palace and surrounded the whole place with his soldiers and didn't let anyone on the opponent's side to enter. When the Queen asked what the commotion was all about, Yushin told her that Bidam betrayed her and planning to start a coup to dethrone her, the Queen didn't believe him at first, but days has passed and Bidam and the rest of the nobles still hasn't shown up. Bidam and the royal nobles who heard of this news was enraged with what they believed was a plan to usurp the throne and gathered their soldiers and supporters to march towards the palace. A messenger then came and reported to the Queen, that the royal nobles, led by Bidam were marching towards the palace with their entire army. The Queen was shocked and disheartened by this news, but Kim Yushin calmed her and told her that "Bidam was a traitor who betrayed his Queen. But fear not! For I, have a plan to quell him". However, not too long after that, the Queen died. Although some story says that Queen Seondeok, may have been killed by one of the soldiers from the coup. Thus, despite Bidam's rebellion being said as one of the biggest in Silla's history – it didn't even last for 10 days, because it wasn't planned.