AceShowbiz - "Pretty Little Liars" showrunner I. Marlene King kept her promise by unveiling "A" in the summer finale. It turns out that [SPOILER ALERT!] "A" is Charles DiLaurentis who transitioned to become Charlotte DiLaurentis and changed her name to CeCe Drake, played by Vanessa Ray.
CeCe was obsessed with Alison and she was abandoned by her father, Mr. DiLaurentis. Her brother Jason didn't recognize her when they met in high school and they started dating. His father (also CeCe's father) didn't recognize her either when Jason brought CeCe home to meet Mr. DiLaurentis.
CeCe hit Ali that night because she was thinking she was Bethany, who was going to hurt Mrs. DiLaurentis. Mona hit Bethany with the shovel, thinking she was Alison. The Liars found out all about CeCe's story as they watched Ali's conversation with CeCe. The girls also learned that Sara Harvey was Red Coat and Black Swan.
The Liars chased CeCe to a rooftop where she threatened to jump, but she eventually turned herself in. The story then jumped ahead five years. Ali's last name is now Rollins and she's teaching. The episode ended with the Liars telling Ali that someone is after her.
To EW, King answered other questions such as who killed Ian in season 2. The answer is Ian killed himself but Mona staged the note and the crime scene. Wilden killed Garrett in season 3 because Garrett knew the former was a dirty cop and was going to tell. CeCe then killed Wilden.
Shana shot Ezra in New York in season 4 and she's also the one who set the fire at the Thornhill Lodge that almost killed the Liars. Ali saved Hanna from the fire, while Sara Harvey saved the other girls.
CeCe was responsible for kidnapping Emily in season 4, because the Liars were close to find out her identity at the time, and she also blew up Toby's house in season 5. CeCe faked Mona's death with a freezing serum and she knocked Jenna unconscious and left her to drown because Jenna knew Ali was alive.
As for the murder of Mrs. DiLaurentis, the case remains a mystery.
"Pretty Little Liars" returns with the remainder of season 6 in early 2016 on ABC Family.