Tomei shared a clip from the show that shows her responding with excitement to the news. She appeared on the episode with Sheryl Sandberg and Kal Penn.
"What an incredible gift to find out about my family's roots with @HenryLouisGates! Eternally grateful for this generation and generations to come.... and the big surprise -- discovering my friend is my REAL cousin! Hey cuz @juliannemoore!!!! Love," Tomei captioned the post.
Tomei and Moore have an identical stretch of DNA on their X chromosome, despite Moore not sharing Tomei's Italian heritage. Moore posted the same video on her own account.
"I KNEW WE WERE ALIKE! @marisatomei is my COUSIN!!" she wrote. "OMG I'm so excited, thank you @henrylouisgates for letting us know we have identical segments of DNA - #FindingYourRoots #twinning."
Tomei and Moore both attended Boston University in Boston, Mass. In addition, the pair both got their start on the CBS soap opera As the World Turns, and co-starred in the 2011 movie Crazy, Stupid, Love.