Rocker Pete Wentz has filed legal papers demanding joint custody of his son with estranged wife Ashlee Simpson.

The singer/actress stunned the pop world when she filed for divorce on February 7, citing "irreconcilable differences."

She asked for primary physical custody of baby Bronx, but Wentz has challenged her request, lodging his response in a Los Angeles court on Monday, exactly one month after his ex. The former Fall Out Boy star has also asked for each party to pay its own legal fees, reports TMZ.com.

Ironically, Wentz claims the couple ended its marriage on February 9 - two days after Simpson filed her divorce petition. She did not specify a break-up date in her court papers.

The couple wed in May 2008.

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