But while Kelly has admitted the pregnancy wasn't planned, she insists she wouldn't change her situation for the world, and is thrilled to have found 'the One' in former rugby player Thom.
Kelly's revelations come as she shows off her pregnancy curves in a tight leopard-print swimsuit as incredibly muscular Thom struts his stuff in the background of the exclusive shots taken in Portugal for Hello! magazine.
Blooming: Kelly Brook shows off her pregnancy curves in a leopard-print swimsuit while her incredibly muscular boyfriend Thom Evans larks around in the background with a water gun
Kelly, 31, told the publication: 'That is what happens when you are in love - you surrender to whatever is to be. It wasn't a plan, but if it happened, it happened. We were boyfriend and girlfriend.'
And in her first interview since announcing the pregnancy, Kelly said the couple have been inseparable since meeting in a London nightclub last November.
She said: 'We have spent virtually every day together ever since. There was no game-playing, which is why I think our relationship progressed so quickly, because we haven't had to deal with egos.
'I love Thom and Thom loves me. We love being together. It is as simple as that.'
Stunning: Kelly has made a career out of her curvy figure, modelling for Ultimo (left) and wearing a tiny red bikini in recent film Piranha 3D but has learned to accept her now changing body
Kelly's confidence in her relationship with Thom comes after splits from actors Jason Statham and Billy Zane as well as Thom's former teammate Danny Cipriani, from whom Kelly split last summer.
The full interview appears in this week's Hello! magazine, out now
But model Kelly said she knew instantly that Thom was 'The One'.
She said: 'I immediately felt he was The One, and I have never felt that before. That has something to do with my age. I didn't want to waste my time with someone I wasn't sure about - it was Thom.'
And while her pregnancy might not have been planned, Kelly says she always knew having a family with Thom was a part of her future.
She explained: 'This baby is not the result of me suddenly becoming broody because I have hit my 30s. It is simply that I have met someone that I am happy to share that responsibility with.'
Kent-born Kelly has been in Los Angeles since the start of January, working on a number of modelling assignments and campaigns, including coming up with designs for a new maternity range for high-street chain New Look.
Former Scotland international star Thom is a former teammate of Kelly's ex Cipriani. He joined Kelly in the U.S. shortly after they met and has been taking acting classes.
Evans played for the London Wasps with Cipriani from 2004 to 2006.
However, the Zimbabwe-born sports hunk was forced to quit his career as a professional rugby player after he suffered a horrific spinal injury. He is now hoping to become an action movie star.