[Grammar] A grammar question on "It was not until..."

[watermen]

I am not sure about the correct grammar of this phrase. For example:

It was not until 2010....

A.did the family reunite
B.that the family reunited

I instinctually answered A when I saw this question. "It was not until 2010 did the family reunite."

However, I was suspicious about my answer after seeing a number of people answering B, thinking twice again, B could be right too, that is why I posted this question here, as I am not sure about the grammar logic behind it.

Which is the grammatically correct answer? and why? Thanks.

 

[2006]

It was not until 2010 that the family reunited. :tick:
Not until 2010 did the family reunite. :tick:

Thanks.

Do understand why?

 

[watermen]

Do understand why?

Are you saying both are correct? I don't understand why, that is why I am posting this question here.

 

[2006]

Are you saying both are correct? I don't understand why, that is why I am posting this question here.

No, only B is correct. A has to be changed the way I changed it in my first response.

 

[watermen]

No, only B is correct. A has to be changed the way I changed it in my first response.

Thanks for pointing out this nuance.:-D