Spencer Matthews, who is also on the brink of parenthood, said they feel "very blessed" that the cousins will be so close in age

London Celebrity Sightings - July 13, 2018
Credit: Neil Mockford/GC Images

Pippa Middleton is expecting her first child with husband James Matthews — but whether they’ll welcome a boy or a girl will remain a mystery for a little while longer.

James’ brother, Spencer Matthews — who is on the brink of becoming a first-time father himself with his wife, model Vogue Williams — recently appeared on U.K. talk show This Morning and talk turned to his new niece or nephew.

“And your brother is about to become a dad as well a little bit after you with Pippa Middleton,” said host Ruth Langsford. “So, do they know if they’re having a boy or a girl?”

“They don’t,” Spencer replied. “They’re extremely private and honestly, we know nothing.”

Pippa is following in the footsteps of her big sister, Kate Middleton, who kept the sex of all three of her children a surprise.

London Celebrity Sightings - July 13, 2018
James Matthews and Pippa Middleton
| Credit: Neil Mockford/GC Images

The reality TV star, 30, added that they feel “very blessed” that the cousins will be so close in age.

RELATED VIDEO: Style Ace! Pregnant Pippa Middleton Steps Out in White Eyelet Dress for Day at Wimbledon

“I think it will be great for the kids to kind of grow up together. We’re all looking forward,” he said.

While Pippa and James are keeping their baby’s sex a surprise, Spencer and Williams are expecting a baby boy — a fact that the model accidentally let slip during a talk show appearance in April.

“I know it’s bad to say, but I was kind of hoping the first child would be a boy so purely if you have girls afterwards, which we’d very much like to have, I always thought it’s nice to have an older brother,” said Spencer.

And he added that they likely won’t stop with one child: “We’d like to have at least three in an ideal world.”

London Celebrity Sightings - July 11, 2018
Pippa Middleton
| Credit: HGL/GC Images

Pippa, 34, officially announced she was pregnant in an article for U.K. supermarket monthly Waitrose Kitchen, where she’s been documenting how she’s keeping up her workout regimen while expecting.

“When I learned the happy news that I was pregnant, I realized I needed to adjust my four to five-day-a-week [fitness] routine,” she wrote, noting that she kept her pregnancy a secret from her gym instructor until the “riskier months” were over.

The younger sister of Kate Middleton was spotted last week leaving a gym session in London on her bike wearing a blue and white striped shirtdress adorned with floral designs. A tie detail above her waist highlighted her growing baby bump.

Of course, Pippa’s baby will also be very close in age to another cousin: Kate and Prince William’s third child, Prince Louis, who was born in April.