Penny Lancaster is leaning over the kitchen table of the LA home she shares with Rod Stewart, making a cardboard fishtail for their three-year-old son. "Stand up on your tippy-toes," Stewart laughingly tells little Aiden, hopping about the floor in one trouser leg, "so that we know how big your merman tail needs to be."
There's warmth and an intimacy to the scene that's notably absent from most Beverly Hills homes, and I'm pretty sure I've never seen anyone look quite as glamorous as Lancaster does with a staple-gun. In addition to joining the cast of ITV's Loose Women - on which Stewart's third wife is to make regular guest appearances - I'm thinking she should try a spell on Blue Peter.
The 43-year-old is a medley of long, honey-brown limbs. In photographs and on red carpets, Lancaster has the ease and confidence of the model she once was, but in the flesh this mother of two is shy and softly spoken, with the reassuring remnants of an Estuary twang and the peculiar meekness of very tall women - as though every move is a silent apology for her extraordinary physique.
I had meant to bide my time before asking the question social media has been buzzing with ever since she was pictured with Stewart at a charity gala in LA last month - her husband's hand placed proudly on her stomach - but I can't help but blurt it out. "No, I'm not pregnant!" laughs Lancaster. "I think Rod did it because I've been on this no-carb diet for two months and have lost 10 lbs."
As a father of eight - with his children Aiden and Alastair (by Lancaster), Renee, Liam, Ruby, Sean, Kimberley and Sarah Stewart ranging in age from three to 50 - it had surprised people that the 69-year-old singer might be looking to expand his family further. Watching this doting dad in his family environment, however, this doesn't seem quite so unlikely.
"Rod loves kids," murmurs Lancaster, once we've sequestered ourselves away in their guesthouse. "But we're definitely done. Aiden took two years to conceive and that gruelling IVF three times over really took it out of me.
Lancaster is enjoying her burgeoning TV career. "What I love most about Loose Women is that it's the kind of chats you have with your girlfriends - where you touch on everything from lighthearted to very serious," she says. She rejects any suggestion that her privileged lifestyle makes her any less easy to relate to than the rest of the panel.
"At the end of the day I'm a mum and an Essex girl and I have the same morals and values as anyone else," she says. But for the next few years, motherhood will remain her priority. "Being a mum is what I do full-time right now. When the boys are both at school every day I will find another career avenue to explore."
With Stewart's schedule as hectic as it is, it's not always easy to keep the children as grounded as the pair would like. "We don't actually have anyone American working for us," says Lancaster, "and our nanny's British."
The couple were reportedly discussing the possibility of moving back to the UK, where they own a property - The Wood House in Epping - which once belonged to Winston Churchill, but for now Lancaster assures me they are "doing quite well as we are, moving the children back and forth".
She and Stewart have a pact never to be more than 10 days apart, so when the rasping rocker goes on tour in Australia early next year, Lancaster and the boys will go with him.
"It means having to take schoolwork with us, but getting an education on the road can be very stimulating and experiencing all those different cultures is important. Every day I'll take the boys to a different museum or gallery and then I'll make sure Alastair does his homework. It might get to the point where I'll have to get a tutor," she shrugs, "but we'll see."
As the Illford-born daughter of a solicitor and a secretary now living a very different lifestyle, Lancaster is mindful of spoiling the boys. "Alastair (9) will often voluntarily give away his birthday or pocket money to WellChild - one of the charities we support. But sometimes if he wants to upgrade something on his iPad I'll say '99 cents is 99 cents. If you want it, you can pay for it.' So I'll write him a list of chores like making the bed or unloading the dishwasher.
"We have housekeepers but I want the boys to be responsible and get that work ethic early. They should grow up believing that they need to get a job, not only to contribute something to society but to be able to wake up in the morning with a purpose instead of just thinking: 'Well, my dad's rich'."
She's less strict with her husband of eight years. "I don't really have to impose any boundaries on Rod," she says, grinning. "Honestly, he hardly has any irritating habits. I mean all those years on stage means that he likes to have the TV on much louder than me. I can literally hear the football commentary on the other side of the house and it drives him mad when I keep turning it down. But I'm very lucky in all sorts of ways: Rod actively enjoys shopping for clothes with me."
Does the famously dapper dresser take longer to get ready than she does? "Well, his hair is a thing," she concedes.
"He has to have the hair right and there might be a few outfit changes before he decides on the final one. Also he's colour blind, so he'll often come out in two different gingham patterns. Then he'll take one look at my face and say: 'Right - I'll go and change.' But I love that Rod takes pride in his appearance."
When Lancaster was dared by a friend to ask Stewart for his autograph at a Christmas party back in 1998, she never imagined that she and the singer - married for five years to the actress Alana Hamilton and six to model Rachel Hunter - would end up making a life together.
People are fond of saying that it's ''hard to believe these two have been together for 15 years''.
Watching them move about their kitchen, predicting each other's movements and offering silent communion through the most banal of tasks, I disagree. And I don't think it's hard to believe that they'll stay together for at another 15, either.