There was a huge scramble at Victoria’s Secret over a $2.5 million diamond bra — after the news leaked that Brazilian bombshell Alessandra Ambrosio would be wearing the pricey undergarment in its big annual catwalk show. The identity of the supermodel wearing the bejeweled “Fantasy Bra” created by London Jewelers each year in the fall extravaganza is always kept a strict secret until a few weeks before the show. VS chiefs had been planning a big reveal in their SoHo store on Thursday. But somebody at the lingerie retailer accidentally posted a sneak peek of Ambrosio in the ornate bra last week in an online video titled “Victoria’s Secret Angels Talk Seduction,” which has been viewed on YouTube nearly 70,000 times. The rumors carried onto Twitter, and then the clip of Ambrosio in the bra was cut from the short film. The show, which will include performances by Justin Bieber and Rihanna, will be taped early next month and screens on CBS on Dec. 4. A Victoria’s Secret rep declined to comment.