The 'Big Little Lies' season 2 finale will break through the secrets the show is built on but we are most curious about the mystery witness Celeste Wright (Nicole Kidman) is set to call in for her custody battle against Mary Louise Wright (Meryl Streep). Celeste took a stand at the end of episode 6 titled 'The Bad Mother' and said that if she was fair game and her character could be questioned by the plaintiff's lawyer, then the same right should be given to her.

She should be allowed to bring in a witness who would be able to bring to light the real side of Mary Louise. However, she did not reveal who the witness would be. Instead, she requested the judge to let her question the mystery witness, considering she is also a lawyer.

After the episode concluded, we have been racking our brains to figure out who the witness could be. The individual has to be someone close to Mary Louise as he/she would have to speak for or in this case, against Mary Louise's character.

While it was speculated that the witness could be one of the Monterey five themselves, we have second thoughts especially after the melodrama the penultimate episode led in with. The finale will lack impact if it were any of the other four women - Madeline Mckenzie (Reese Witherspoon), Renata Klein (Laura Dern), Bonnie Carlson (Zoe Kravitz) or Jane Chapman (Shailene Woodley). So that brings us back to square one. Who could it really be?

That's when it struck us that 'The Bad Mother' in question could be Mary Louise herself. We can think of nothing else but the mystery behind why Perry Wright (Alexander Skarsgard) had moved out after the death of his brother, and why Mary Louise's husband also abandoned her. Does this mean Celeste knows of something she hasn't revealed as of now? 

We did, of course, come across fan theories about who the mystery witness could be and many believe it is none other than the husband who abandoned Mary Louise. The theory is based on IMDb's synopsis of the episode which reads, "Celeste questions Mary Louise about a tragic event from Perry's childhood; Madeline worries their lie is tearing the Monterey Five apart."

The tragic event referenced here has to be related to Perry's brother Raymond's death. There are two possibilities at this point. The first is that Mary Louise actually killed her son, Raymond, leading Perry to move away from her as soon as possible. Second, Perry could be the one who caused his brother's death which Mary Louise then covered up leading to her husband abandoning her.

Many are rooting for the first theory because that would also explain Perry's hatred for women. It could be a result of trauma from watching his mother kill his twin brother. Either way, Mary Louise is in deep sh*t. 

Earlier in the season, Mary Louise had even spoken about Raymond and said, "Right after the accident, right after we lost Raymond, I was sure I would not be able to go on. I was never sure about anything in my whole life, that I wouldn't go on, but I did. Because of Perry."

While multiple Redditors agree with the above two possibilities, Redditor u/thebenswain posted a long note about the episode and convincingly theorized, "For me, especially now knowing that Mary Louise will have to answer to what kind of mother she was, I felt like that was a pretty solid indication that we'll find out that, in a way, Perry's violence towards women was overdue violence towards his mother. If we think about it, everyone's life has been about fighting against what their parents were. Maddie is fighting hard to find a way to value her marriage to avoid being like her parents. Renata has become rich to avoid being poor like her parents. Bonnie tried to run away from being like her mom. And so on."

The user also added, "I think it sets up perfectly for Mary Louise to actually get her wish, which isn't AT ALL to have custody of the kids, but to paint her son as a sympathetic figure who was more of a victim than an aggressor. Maybe that's what was up with the smile when she was called to the stand. Not a nervous smile after all, but a 'this is even better!' smile."

The finale of HBO's 'Big Little Lies' will air Sunday, July 21 at 9 p.m.