Supergirl's uneven third season ended with some major reveals as well as some major questions (including a second, Russian Supergirl), which means that there are big changes to come in the upcoming season. We lost Winn, but we gained Brainiac. J'onn stepped down, but Alex stepped up. Mon-El has departed, but is it really forever? And what exactly is Lena up to now? The show's EPs addressed some of this after the Season 3 finale, but there's still so much that we have yet to learn ... check out the new trailer below, which gives a glimpse of how some of that may play out (intensely!)

Supergirl returns Sundays this fall on The CW; check out the series synopsis below:

SUPERGIRL is an action-adventure drama based on the DC character Kara Zor-El, (Melissa Benoist). Twelve-year-old Kara escaped the doomed planet Krypton and was sent to Earth where she was raised by a foster family. Kara grew up in the shadow of her foster sister, Alex (Chyler Leigh), and learned to conceal the phenomenal powers she shares with her famous cousin, Superman, in order to keep her identity a secret. Years later, Kara was living in National City and still concealing her powers, when a plane crash threatened Alex’s life and Kara took to the sky to save her. Now, Kara balances her work as a reporter for CatCo Worldwide Media with her work for the Department of Extra-Normal Operations (DEO), a super-secret government organization whose mission is to keep National City – and the Earth – safe from sinister threats. As Kara struggles to navigate her relationships and her burgeoning life as a reporter, her heart soars as she takes to the skies as Supergirl. Based on characters created by Jerry Siegel and Joe Shuster, SUPERGIRL is from Berlanti Productions in association with Warner Bros. Television, with executive producers Greg Berlanti (“The Flash,” “Arrow”), Sarah Schechter (“Arrow,” “The Flash”), Robert Rovner (“Private Practice,” “Dallas”) and Jessica Queller (“Gilmore Girls,” “Gossip Girl,” “Felicity”).