Amanda Seyfried opens up about Peacock's "Long Bright River," her 40th birthday plans and what song she most wants to hear in "Mamma Mia 3."

For Amanda Seyfried, the Peacock limited series offered a rare opportunity to play a character adapted from a book while working closely alongside the author, Liz Moore.

Amanda Seyfried says there were two major reasons why she wanted to star in Peacock's adaptation of Liz Moore's best-selling novel "Long Bright River" -- the location and the fact it cast her against type.