A father-to-be fed a watermelon to a hungry hippo to reveal the sex of his child. The reveal happened Saturday at Capital of Texas Zoo in Cedar Creek. Blue Jell-O poured out of Tank the hippo’s mouth, indicating the couple is having a boy. But not everyone thinks getting the hippo involved was a good thing. “Worst gender reveal,” was one tweet. “That person's baby is not important enough to feed a hippo food coloring,” goes another comment. But the zoo said the gender reveal wasn’t a rogue incident — and they helped the expecting parents safely organized the celebration. Zoo director Michael Hicks said one of the workers often gives Tank watermelons with different flavors of Jell-O inside as a treat. So when the couple wanted to do a gender reveal, the zoo invited them to borrow the 5-year-old hippo to help with the surprise. “This is the same Jell-O people feed their kids. It’s totally harmless,” Hicks told The Post.