Melissa Leo, Rosie O'Donnell join Mark Ruffalo's HBO series

Oscar winner Melissa Leo and actor-comedian Rosie O'Donnell have boarded the cast of Mark Ruffalo's HBO limited series "I Know This Much Is True".

The six-episode series is based on Wally Lamb's New York Times bestseller of the same name, reported Variety.

It is described as a family saga that follows the parallel lives of identical twin brothers in an epic story of betrayal, sacrifice, and forgiveness, set against the backdrop of 20th century America.

Derek Cianfrance, best known for films such as "Blue Valentine" and "The Place Beyond the Pines", is serving as writer and executive producer as well as director.

Ruffalo, 51, stars as twin brothers Dominick and Thomas Birdsey. The actor is also executive producing the show.

Leo, 58, is playing Ma, full name Concettina Ipolita Tempesta Birdsey, the mother of the twins, while 57-year-old O'Donnell will star as Lisa Sheffer, a social worker at the Hatch Forensic Institute.

The cast also includes actors Archie Panjabi, Imogen Poots, Juliette Lewis and Kathryn Hahn.

Lamb, Ben Browning, Glen Basner, Gregg Fienberg, Anya Epstein and Lynette Howell Taylor are also executive producing the show.