The stars fell out after the actor began dating Farrah Fawcett in the late 1970s, but reunited following her death in 2009.
They tried to tackle their issues on a reality TV show for Oprah Winfrey's OWN network, but the series was a flop and was soon axed - leaving their relationship worse off than before.
The Love Story star documents their tumultuous past in his new tell-all tome, Both Of Us: My Life With Farrah, and decided to send Tatum a copy as she attempted to beat her long-running drug problems at a treatment centre earlier this year (12).
He tells the New York Post, ""I sent it. She waited a week then texted her OK. She's doesn't come off well (in the book).
""Tatum's complicated. I think she'll come out of rehab fine but, then, I thought that before.""