Mark has been married to outspoken Katie for four years and they have three children together, daughters India and Poppy and son Maximilian.
But while most people she meets are terrified of her, Mark has revealed there is a much softer side to the former Apprentice star.
Speaking to The Sun On Sunday, Mark said: "She terrifies everyone except me.
"The Katie - the one joking around wearing a onesie - is the one I see at home every day. She has a softer, more affectionate side."
He added: "I was worried about Katie going into the house - and I still am - because the show was always going to set her up to clash with people.
"I have been watching from behind the sofa at times in case Katie blurts something out in the house and then gets thrown to the wolves."
Earlier today, it was revealed that Katie is one of four housemates facing eviction this week.
Viewers have seen her repeatedly come to blows with US blogger Perez Hilton, however the dynamic has suddenly changed following his 'surprise departure'.
Yesterday, Perez staged a fake walk out as part of a secret CBB task.
Along with her fellow housemates, Katie was told that Perez had decided to quit and would not be returning to the Channel 5 show.
Sparks are set to fly, however, as what they don't realise is that Perez is holed up in a secret room next door - and is watching their every move. Uh oh!