James Mangold and Boyd Holbrook talk about how the discovery of Johnny Cash and Bob Dylan’s letters led to a major book change in A Complete Unknown.

As shown in A Complete Unknown, singers Bob Dylan and Johnny Cash created a friendship in real life, but some true details are altered or left out.

The filmmaker first tackled the life of Johnny Cash in 2005's Walk the Line, which garnered tons of acclaim, including an Oscar win for Reese Witherspoon and a nomination for Joaquin Phoenix. Now, Mangold returns to Cash in A Complete Unknown, another musical biopic, this time centered on the rise of a young Bob Dylan ( Timothée Chalamet ).