AS French Revolution help!

Hi, I'm currently studying for my AS History exam on the French Revolution and there's one particular bit that I don't quite know how to explain if the question comes up.

There is potential for there to be a question on 'why did the privileged orders oppose the government?'. I understand that they were reluctant to accept proposed financial reform, as they had the most to lose, but I don't understand why they then decided to support the Third Estate in 1789, by joining them in the formation of the National Assembly?! Surely this just goes against their previous standpoint? Was Louis' exiling of the Paris Parliament the turning point for the privileged orders? Why did they suddenly decide to show sympathy after so many years of opposition..?

Hi Becki, it's Rhiannon!
I think I basically asked Mr, Wallinger the same question to not much prevail but I think he told me it was basically the privileged orders now hated the King as well as the third estate and so joined them in forming the national assembly was, in their opinion, one way to try and restrict his power at least. Also, is there any relevance to the fact he was sending troops everywhere and people were rioting, weren't they concerned about their homes or something? And I assume they wouldn't want to anger the third estate after the Bastille etc. so joined them instead. Well I hope that helps a bit anyway