TMZ has learned ... Ashlee Simpson just filed for divorce from hubby Pete Wentz.
In documents filed in L.A. County Superior Court, Simpson cites "irreconcilable differences" as the reason for the divorce.
She's asking for joint legal custody and primary physical custody of two-year-old Bronx.
Simpson, who is repped by disso queen Laura Wasser, is also asking for spousal and child support. Wentz is repped by Stacy Phillips.
Sources tell TMZ there is no prenup. The couple married in May, 2008.
The couple just released a joint statement, saying, "After careful consideration, we have made the difficult decision to file for divorce.
We remain friends and deeply committed and loving parents to our son Bronx, whose happiness and well-being remains our number one priority. We ask that everyone honor our privacy as we navigate this next phase of our lives."