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Channing Tatum ’s getting raw about his messy split from Jenna Dewan ... calling it so brutal, the heartbreak actually fueled his latest gritty movie role.

The actor opened up about stepping into the shoes of real-life fugitive Jeffrey Manchester for his new movie "Roofman" -- especially the gut-punch moment when his character longs for his daughter -- admitting he could tap into that pain firsthand, thanks to his breakup with Jenna. Gallery Launch Gallery Getty

Channing -- who met Jenna on the "Step Up" set in 2006, married her 3 years later, before they separated in '18 -- admitted to Variety it was crushing to watch their love story unravel, especially since they were still so young when it all began.

He said they fought hard to keep things together, but it

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