N.E.R.D. lead singer and esteemed producer Pharrell Williams is gonna have to add diaper changer to his list of credentials -- he's gonna be a dad! His baby mama is a "model type who he met with friends in Miami this year," Page Six reports. An insider says the woman "is very pregnant and travels with him. She hangs out with the backstage crew when he performs." Still, Pharrell is mum on the subject: "Pharrell is extremely private and won't release any details," the pal says. Somehow, we don't think he'll be able to "Have It Like That" forever…