Season 6B of ABC Family's "Pretty Little Liars" will feature a time-jump that will see the Liars – Aria, Emily, Hanna and Spencer – getting involved in yet another mystery that is even more dangerous than Charlotte's A game.

"Pretty Little Liars" executive producer Marlene King has been dropping hints about the second half of the season on her Twitter account, and she recently revealed that she's not yet done with the twin theory from Sara Shepard's series of book, which is the source material for the television series.

Reacting to a fan's query on why she keeps hinting at a twin theory and if the twin twist will be featured in season 6B, King wrote: "The story isn't over. @aguerin32 #Twins."

In Shepard's book, Alison has a twin named Courtney DiLaurentis, who is admitted to Radley Sanitarium for behavioural problems. In the television series, the twin theory is yet to materialise, but spoilers indicate that one of the leads will have a twin in season 6B.

Not much is immediately known about the twin, but King had hinted about it in a previous interview with ETOnline, saying there's a reason why the show keeps dropping the twin hints.

"There is a reason why we keep dropping these not-so-subtle clues about the twins, so I would say wait for it," King told the media outlet. "Wait for it. You're not going to see Courtney, but you may see double of someone."

Soon after, Charles was introduced as Jason and Alison's sibling, and it was assumed that Jason and Charles, who later transitioned into Charlotte, were twins. However, Mr. DiLaurentis revealed in one of the 6A episodes that Charles is Jason's older brother.

It will be interesting to see how the second half of the season introduces the twin theory, which was one of the crucial elements in Shepard's books.

As for what to expect in the second half of the season, King described the premiere as "hard." She also revealed to her Twitter followers that season 6 finale was in the works. "I'm working on the next finale. Time flies when you are having fun in Rosewood," King tweeted.