There’s a joke among the staff that Kate treats William as the fourth because he occasionally behaves like one,” Tom Quinn claimed.

Though Prince William is next in line for the throne, Kate Middleton's husband still has some growing up to do. In a new interview, author Tom Quinn discussed his new book Yes, Ma’am: The Secret Life of Royal Servants and revealed there's a portion of the tome that mentions how the dad-of-three can sometimes be immature behind palace doors.