Simon Cowell's Ex-Fiancee -- I'm HAPPY For Him ... No Really

Simon Cowell's ex-fiancée is doing something rarely seen in Hollywood -- treating his baby news like a bonafide adult because she's actually HAPPY for him ... sources tell TMZ.

After news broke Cowell knocked up Lauren Silverman ... it was reported that his ex-fiancée of two years Mezhgan Hussainy was devastated, thinking it should have been her.

Sources close to Mezhgan tell us, that couldn't be further from the truth. She and Simon have remained close since their split -- they're good friends and talk almost every day.

In fact, Simon told Mezhgan about the baby weeks ago -- and she immediately called Lauren, who she's also friends with, to offer her congrats and support ... knowing how stressful the media attention can be.

Bottom line: she's thrilled for the couple. As long as Simon's happy, she's happy.