What happened to Sanji in Zou? The current situation of Sanji has not been made clear so far in the manga. The following is a summary of the pointers.


Sanji is the only person in the SH crew who is wanted Alive and not Alive/Dead. 
His bounty has increased only by a 100 million Berries (to 177m berries ) which suggested that he was involved in any earth shaking event at Zou. 
Nami is seen crying when she says to Luffy, "I'm sorry about Sanji" and there is nothing added on to it. 
Brook says, "I'm so sorry about what happened to Sanji san. I can't even face you right now".
Strangely Luffy and crew are not at all worried about Sanji and don't feel obliged to go to his aid.
In the last seen image of Sanji he is seen tacking cannon balls from some ship and before that he defeats the Kaido crew pirate Sheepshed. 


Considering the above, I like to know some plausible theories on the current condition of Sanji.
Sanji was taken from Zou by Capone Bege as per Big Mum's instructions, and invited to his own wedding, a diplomatic marriage between Sanji, the third son of the Vinsmoke family and Purin, the 35th daughter of the Charlotte (Big Mum) family.