which card was it?

There are three friends Mr.A, Mr.B and Mr.C. Mr.C takes out 16 cards from a pack of cards which are as under:-

Hearts: A, Q,4.
Spades:J,8,4,2,7,3
Club: K,Q,5,4,6
Diamonds: A,5.

All the three persons know these 16 cards which are taken out.

Shri C inverts all the cards and shuffles them. He now takes out one card from the pack of 16 cards, in the presence of A and B,  without revealing the card either to A or B. He then inform  only the number to Mr.A( not the colour).(of course is not informed).
Thereafter he goes to Mr.B and and informs him about the colour of the card.

He then asks the Both A and B( when both A and B are present and hear each other) as to which card from the pack of 16 was taken out.The following reply is furnished by them

First A: I do not know
Then B: I knew you do  not know
Then A: Now I know
Then B: Now I also know.

which card was it