HBO has yet another limited series with a star-studded cast in the works.

The miniseries "I Know This Much Is True" has added Kathryn Hahn.

"I Know This Much Is True" is based on the 1998 novel of the same name by Wally Lamb. Both follow the lives of twin brothers, Dominick and Thomas Birdsey, one of whom suffers from paranoid schizophrenia. Ruffalo is pulling double duty and portraying the two characters.

Leo signed on to play Concettina Ipolita Tempesta Birdsey, the mother of the twins. Meanwhile, O'Donnell has ed as Lisa Sheffer, Thomas's friend and social worker. Both actresses have been lauded over the years; Leo won an Academy Award in 2010 for her role in "The Equalizer 2," while O'Donnell last starred in 2009's "America."

The script for the limited series was adapted by Derek Cian, who is also directing the series. He is an executive producer alongside Lamb, Ruffalo, FilmNation Entertainment's Ben Browning and Glen Basner, Gregg Fienberg, Anya Epistein, and Lynette Howard Taylor. Jamie Patricof is co-executive producing.

The show's premiere date has not yet been announced.

[via: Variety]