The sudden drug-related death of DJ Adam “AM” Goldstein has left the celebrity spinner’s former fiancee, socialite Nicole Richie, overcome with despair. Nicole is struggling to cope with the death of her ex as she prepares to welcome her second child with Good Charlotte rocker Joel Madden, spywitnesses say.

“Nicole almost collapsed in grief when she found out,” an insider tells Star. “She said she felt like her heart stopped for a few minutes.”

The former couple bonded over their battles against addiction — crack for Adam, heroin for Nicole — and were briefly engaged to marry in 2005. Adam went on to date singer Mandy Moore.

“Adam was the one who got her to straighten up,” says a source. “She never thought he’d come to this. She’s horrified and regrets that she didn’t reach out and help him.”

Nicole has been under a doctor’s care since learning of Adam’s death in New York City last Friday.