If there's one thing we all know about Grey's Anatomy, it's that Dr. Meredith Grey is one of the most complex characters to ever be on television. Like, what a coincidence that she's been weirdly related to some of the other surgeons. However, fans are specifically interested in her relation to Dr. Maggie Pierce.
Turns out, Maggie (played by Kelly McCreary) and Meredith (played by Ellen Pompeo) are half-sisters! In the Season 10 finale of the medical drama, it was revealed that Maggie's parents are Dr. Richard Weber (played by James Pickens Jr.) and Ellis Grey (Kate Burton), so the girls share the same mother.
Ellis had a fling with Richard when Meredith was five years old, which led to them having a baby. However, they secretly put her up for adoption, so Maggie never knew who her real parents were. After looking into it as an adult, Maggie learned that her mother was dead, but was a famed surgeon at Seattle Grace Hospital, which is why she took on the role as department head of cardiothoracic surgery there.
But, Maggie didn't know Richard was her father, and when he found out (after all that time of not knowing), he hid the news from her for some time. Understandably, when he told her, she was extremely upset. Meredith was also shocked to find out that Maggie was her half-sister, and the two had a rather strange relationship for a while before finally becoming close. Meredith was mostly confused because she felt like she would have remembered her mother being pregnant when she was five years old, but a flashback later helped her remember the moment her mom gave birth to Maggie. So crazy!
And as if that relationship isn't mind-blowing enough, Meredith also had another half-sister on the show long before Maggie. Lexie Grey (played by Chyler Leigh) sadly died in the plane crash at the end of Season 8. She was the daughter of Meredith's dad, Thatcher Grey, and his second wife, Susan Grey, and she didn't find out about her older sister Mer until she was a medical student at Harvard. Lexie then became an intern at Seattle Grace right before Meredith began her residency and the two were super close.
Thatcher and Susan also have an older daughter, Molly Thompson, who is Lexie's sister and Meredith's half-sister. Additionally, Meredith is very close with her sister-in-law Amelia Shepherd — she lives with Mer and Maggie! — who is her late husband Derek Shepherd's younger sister. We seriously can't keep up with Meredith's complex family tree!