The sub-aqua spectacle marked two significant events for the singer / songwriter and his Canadian actress wife — their second wedding anniversary and World Water Day.
"It was a lovely way to celebrate our marriage and do something that was going to be beneficial to other people" said Darius, who returned to his native Scotland for the shoot, which was organised by award-winning celebrity photographer Candice.
Founder of the charity fresh20, Candice highlights the charity's aim to provide clean drinking water to the world's poorest nations through striking underwater shots featuring celebrities including Keira Knightley, Lily Cole and Kelly Brook.
Natasha was so inspired by the work Candice was doing with fresh20 that she personally funded the building of a well in a village in Madagascar, which now provides clean water for about 3,000 people.
"It was a really lovely thing to talk to my kids about and show them how you can genuinely change people's lives," she tells HELLO! "I've been kept constantly updated with the progress of it all, so they get to see photos and letters from people in the village."
Darius became an ambassador for the charity two years ago and jumped at the change of diving into the deep end with Natasha at Edinburgh's Royal Commonwealth Pool.
"I could have stayed in there until eight o'clock at night - it was fantastic," said Darius, who managed to catch up with family and friends while back home.
"It was surreal and all the more so because you couldn't really see what was happening other than the blotchy outline of Candice's hand, trying to work out if it was thumbs-up or thumbs-down. And just at the point when you thought everything was set up, one of Natasha's skirts would float up and cover your face or part of the set behind you would flap around."
For more details and images from the exclusive shoot see HELLO! Magazine, out now!