Jessica Simpson Involved in Pregnancy COVER-UP

12/26/2012 1:45 PM PST

Jessica Simpson is hiding something -- because the newly pregnant singer just hit the beach in Hawaii ... wearing an enormous green cover-up thing.

Just one day after announcing her new bun in the oven, Jessica went out for a waterfront stroll today with her fiance Eric Johnson ... and her rapidly-forming fetus. 

This will be Jessica's second child after she gave birth to her daughter Maxwell in May.

As we reported, Weight Watchers will continue their partnership with Jessica despite her new pregnancy ... and inevitable weight gain.