The grown-up Harry Potter star pranked the child minder by convincing her to be her nanny as comedienne DeGeneres told the actress what to say and do via an earpiece.

Emma told the woman, who had no idea what was going on, she was "very particular", listing her likes and dislikes as if she was a little child.

These included: "I don't like crusts on my sandwiches", and "I like to go potty alone".

Ellen then instructed her guest to laugh manically, sob and stare at the confused hopeful after stating, "I want to be able to trust you with my secrets".

Emma also threw a tantrum after receiving bad news via a text and hurled her cell phone across the room, while sucking on a huge lollipop.

When the Brit, who was on the show promoting her new film Beauty & the Beast, eventually revealed the nanny was being pranked, the child minder seemed relieved, admitting she was "very confused" about what was going on.

The skit appears on The Ellen DeGeneres Show on Friday (03Mar17).