They are “overjoyed with this news and they look forward to welcoming this newest addition into their family,” the rep adds in a statement.
Willis, already has three daughters with first wife Demi Moore: Rumer, 23, Scout, 20, and Tallulah, 17.
A few months after their March 2009 wedding in the Turks and Caicos Islands, Willis told Us Weekly he wasn’t sure about becoming a dad for the fourth time. “It’s been suggested we begin breeding immediately,” Willis joked. “[But we’re taking it] just a day at a time. Really slowly.”