One of the longest-running mysteries will be finally solved on the next episode of "Pretty Little Liars" season 7.

The trailer of the upcoming episode titled "Power Play" reveals that the culprit of Mrs. DiLaurentis' (Andrea Parker) murder will be finally revealed as her daughter Alison (Sasha Pieterse) takes her turn to play the deadly board game sent to the Liars by A.D.

Aside from finding out who killed her mother, Ali will also be forced to make a major personal decision as she takes her turn in playing the game. According to the episode's synopsis, her decision making will be extra difficult after A.D. prompts her to remember a trauma from her past that she opted to forget.

Meanwhile, the Hastings will also be involved in their own family drama as Spencer's (Troian Bellisario) father Peter (Nolan North) returns to Rosewood. Spencer will reportedly confront her father regarding his past mistakes and ask him his recent whereabouts.

On the other hand, Emily (Shay Mitchell) will still struggle dealing with Ali and Paige (Lindsey Shaw) at work in Rosewood High. Since she and Paige began working back in their old high school, both Ali and Paige made it clear that they have no intentions of having a cordial working relationship with each other.

Also, the upcoming episode will show that Aria (Lucy Hale) will still be left in the dark regarding the status of her relationship with Ezra (Ian Harding). It will be aggravated due to A.D.'s continuous taunts.

But according to Ashley Benson, the actress who portrays the role of Hanna in the series, fans will learn about the endgame of all relationships in the final episodes of "Pretty Little Liars" season 7. "I think all the relationships will find their way, good or bad, but there's never going to be any bad blood between any couple if they don't end up together," Benson states in an interview with E! News.

The next episode of "Pretty Little Liars" season 7 will air on Freeform on Tuesday, May 9, at 8 p.m. EDT.