NCIS: Los Angeles reaches a notable accomplishment when its 100th episode airs this week.

In anticipation of the milestone, creator and executive producer Shane Brennan jumped on the phone to speak with TV Fanatic about this pivotal episode, "Reznikov, N.," along with the next installment in Callen's family history.

Check back after the episode airs for our full review and then on Wednesday for more from Brennan regarding what's to come for Deeks and Kensi the rest of the season. And read on for excerpts from my exclusive Q&A with the producer...

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TV Fanatic: Congratulations on 100 episodes. The show's in syndication already, so what does this milestone mean for you?

Shane Brennan: What I hope is that anyone who has sampled the show in syndication will decide to come --and who hasn't watched it on CBS -- will come to CBS for the 100th episode and say "Wow. I've got to see how that all happened." 

The 100th episode pays off a lot, if not all, of the back stories that we've set up for Callen. This is an episode that I conceived way back at episode 25. So, I've been waiting 75 episodes to tell this story. It's been a lot of fun building the puzzle. Every time we do a Callen story, there's a little bit more in that story that reveals what's about to unfold in the 100th episode.

Callen's struggles with his identity and family history has been a continuous thread throughout the seasons. Why the decision to bring that back to the forefront in the 100th episode?

It actually goes back to the conception of the series. What struck me when I was talking to undercover NCIS agents -- I went down to Washington and met a whole bunch of them --and I was looking for some sort of theme for the show and what struck me was it's about identity. When you are undercover you are playing someone else. You have sometimes multiple identities and as a theme for one of our characters I thought that would be a good thing to give Callen.

Someone who is very good at being undercover because he's been many different people because he doesn't know who he really is, so each of the characters that he turns to -- he dips into a well of all of these aliases and all of these people that he plays and they are all based on the foster homes that he spent time in. So, in each of those foster homes he tried to fit into the family by becoming one of them. So he had an unconscious training to be someone who is incredibly good undercover. 

But the sad reality is that he still doesn't know who he is. So for me, that was a great theme to play through this entire series with that character and what we've done where we can is reveal more and more about his back story and who he is. And, so his is a journey to discuss who he is in a very literal sense.

Will the"G" be revealed?

The "G" will finally be revealed. I'm not going to tell you whether it's revealed in the 100th episode. There is someone in the episode who looks him in the eyes and says, "I am your father."

Last season, it was revealed that Hetty had this group of orphans that she brought into NCIS and Callen was one of those. Will this story provide more insight into Hetty's story at all? 

It does in the sense that Callen is Hetty's favorite. There's no getting around that. There's a responsibility that Hetty feels for Callen because Hetty knew his mother and feels some guilt and responsibility because she couldn't get there. She didn't get to that beach in Romania and Callen's mother was killed in front of him.

There's always been in Hetty's mind a responsibility for this orphan. And, when it's revealed that Callen's father is alive and has been kidnapped, she is trying to protect him. She knows what he's going to do. She knows how he's going to respond and she tries to stop that from happening. She knows that he's vulnerable when it's personal. And, he does find himself.

What will be the 100th episode format?

The audience will watch the first minute and a half and they will have to watch the rest. We open the show with the end. And, then after the credits we begin eight hours earlier and then work our way through the episode up to that point. And, in the first minute and a half, you see that things have not gone well at all.

You don't see Callen in that first 30 seconds, but you do see Sam and you do see Granger and things are as bad as they could possibly be. It's a very powerful episode. It's very, very powerful emotionally for Callen. And, the story just rockets along. There is a lot for everyone who has watched 99 episodes. There's a lot for them to watch. It will be very satisfying for those audience members who have followed the show.

By the way, Chris O'Donnell in this episode -- everyone who's seen the episode they all say the same thing, "Chris is phenomenal." This is the best work he's done on the series. To give you an example, the last three minutes of the show, Chris is there by himself, he says two words in the whole three minutes. And, it's the most powerful thing he's ever done on the series. It's fantastic to watch.

Will Callen be able to come out of it in a better place than he has been in most of his life?

Yeah. He does come out in a better place. As I said, those last three minutes are incredibly powerful. It's very very very moving. You will feel good for Callen. It's both sad and uplifting.

Here is a look at the first 90 seconds of the special episode:

Carla Day is a staff writer for TV Fanatic. Follow her on Twitter and on Google+.