Blake Lively

Surprise!!! Blake Lively is expecting once again, and she shocked everyone by visually announcing her 4th baby with Ryan Reynolds.

Blake was attending the 10th Annual Forbes Power Women’s Summit Thursday in NYC … she entered the event and posed for pics, proudly showing off the upcoming addition to the fam.

Witnesses at the event tell TMZ … employees only let a few photogs shoot Blake — telling them beforehand that this would be a "sensitive shoot," adding they’d know why when she walks down the red carpet.

Boy, were they right! Blake’s noticeably pregnant, but it’s unclear how far along she is.

Blake posted a swimsuit pic a few weeks ago — though we don’t know when it was taken — and there was no bump in sight … possibly intended to throw people off before the big reveal.

Blake Lively and Ryan Reynolds Together

Blake and Ryan have 3 kids together already — 7-year-old James, 5-year-old Inez, and 2-year-old Betty.