"It has been quite hard to keep it under wraps," says Terri. "We haven’t told many people. It’s going to become so much more real when everyone knows. We were trying to get pregnant so this is the best news ever."
Clark, who’s from North Wales, adds: "To start with it was quite a lot to get my head around – it’s such a life-changing event – but now I can’t wait to be a dad and start my family with Terri. She has just started to show and it’s very exciting."
Terri Seymour and Clark Mallon
The couple have been together for three years, after being introduced by HELLO's contributing style editor Donna Air at her birthday party in London.
The couple decided that until the first trimester of the pregnancy was complete they would keep their baby news a secret to all but their nearest and dearest, who included not only Terri’s mum Margaret and her and Clark’s closest family members, but also Terri’s ex-boyfriend and best friend Simon Cowell.
"He’s so thrilled for us," Terri says. "We were having dinner in LA and I told him and he was over the moon. Actually immediately after congratulating me the first thing he said was he had to be the godfather.
"Then he said it was perfect timing with his son Eric being so young and he hoped I would have a baby girl so he could set her up with Eric and they could date. ‘How perfect would that be,’ he said. Typical Simon."
Terri says she made Simon promise not to tell his girlfriend Lauren Silverman as she wanted to tell her herself. "Amazingly, he managed to keep it a secret – he’s usually terrible at keeping them so I wasn’t sure he’d be able to do it," says Terri.
Lauren managed to help 'cover' Terri’s bump when the friends, along with X Factor host Dermot O’Leary, attended a One Direction concert at the Rose Bowl in Los Angeles earlier this month, with a picture posted on Twitter showing Lauren hugging Terri.
"She was covering up my belly area nicely," laughs Terri.
Read the full interview in HELLO! magazine out now.