BBC interview dad reveals exactly what caused his kids to burst into the room

Speaking to The Wall Street Journal, Kelly said he forgot to lock his study door, which allowed his daughter Marion and eight-month-old brother James to dart into the room.

The two children had been watching the interview on TV with their mother – who was filming it on her phone – and recognised the room and went to find dad.

And the reason Marion bounded in so fantastically full of life? It was her birthday and she’d just celebrated it at her school. “She was in a hippity-hoppity mood that day because of the school party,” Kelly said.

Soon after her brother James wheeled into the room. However, mother Kim Jung-A only then realised the kids were missing when seeing them on TV.

Kim said: “He usually locks the door... Most of the time they come back to me after they find the locked door. But they didn’t. And then I saw the door was open. It was chaos for me.”

But fortunately Kelly saw the funny side: “I saw the video like everybody else. My wife did a great job cleaning up a really unanticipated situation as best she possibly could," he said.

“It was funny. If you watch the tape I was sort of struggling to keep my own laughs down. They’re little kids and that’s how things are... I made this minor mistake that turned my family into YouTube stars. It’s pretty ridiculous.”

He also answered the most important question about the video: yes, Prof Kelly was wearing trousers, albeit jeans beneath his suit and tie.

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Menendez also asked the couple how they reacted to many assuming Kim was a nanny and not the mother. Although Kelly said he felt “pretty uncomfortable” about it, his wife was more relaxed: “I hope people just enjoy it and don’t argue over this thing,” she said. “I’m not the nanny – that’s the truth – so I hope they stop arguing.”