Montag walked out on her husband of two years in May and filed a divorce petition in Santa Monica, Calif. Superior Court last month, citing irreconcilable differences.
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Pratt signed off on the papers after he was served last week and the divorce will be finalized in six months.
Montag's lawyer, Jodeane Farrell, tells TMZ.com, "Both Heidi and Spencer are in agreement to settle their divorce as quickly as possible without the need of a court appearance."
The ex-couple wed in Mexico in 2008 and exchanged vows for a second time on "The Hills" in 2009 amid claims their initial nuptials were not legally binding.