According to legal docs obtained by TMZ ... Fergie's asking the judge to restore her former name. She made the request in divorce docs where she also asks that the judge terminate the court's ability to award support for both her and Josh Duhamel.

TMZ broke the story ... she legally switched to her stage name -- Fergie Duhamel -- back in August 2013. At the time she had been married to Josh for nearly 5 years.

As we first reported ... Fergie filed for divorce on Friday. It came as no surprise at the time ... they've been apart publicly since September 2017 when they announced they were breaking up. According to the new docs ... the couple lists the date of separation as April 1, 2017.

Fergie's also asking for joint and legal custody of their 5-year-old son, Axl.