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Britney Spears is reflecting on her latest marriage ... blasting her short-lived nuptials to Sam Asghari as a bunch of B.S.

The singer sounded off on her third failed marriage on Instagram Sunday, where she claimed the only reason she wed the model was to distract herself from her then-estrangement with her sons, Sean and Jayden .

Per Brit, the wedding took place during the "hardest years" of her life ... as she was allegedly "cut off" from communicating with her boys, Sean Preston and Jayden James, who she had with ex-husband Kevin Federline in 2005 and 2006, respectively.

She wrote ... "It's weird me and Sam were married but it almost felt like a fake distraction to help me deal with it." Gallery Launch Gallery

Remember, Britney and Sam tied the

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