The couple filed for divorce in December 2010 after being married for just over two years.
"It was horrible," Johansson told Vogue. "Of course it's horrible. It was devastating.
"It really throws you. You think that your life is going to be one way, and then, for various reasons or whatever, it doesn't work out."
Johansson continued that she "never thought" she would be getting divorced, adding: "And there's no way to navigate it. Nobody can give you the right answer. It's never anything you want to hear. It's a very lonely thing. It's like the loneliest thing you'll ever do, in some way."
The actress explained that her split from Reynolds was "comically amicable" and described her marriage as "a beautiful thing".
She also revealed that she is still recovering from the break-up, saying: "I don't feel on the other side of it completely, but it gets better. It's still there. More than anything, it's just that not having your buddy around all the time is weird. There's no rule book. I think it's just time."
Since her split from Reynolds, Johansson has been linked to stars such as Sean Penn, Bradley Cooper and British musician Dan White.
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