Stella McCartney chose the launch of her spring/summer collection in Paris yesterday to announce that she is three months pregnant with her first child.

She married Alasdhair Willis on the Mull of Kintyre in August last year, and their baby – due next April or May – will be Sir Paul McCartney’s third grandchild. The former Beatle is currently in America with his second wife, Heather. Their daughter, Beatrice, will celebrate her first birthday at the end of this month.

Ms. McCartney, 33, said she did not know if she was expecting a boy or girl.

“I want it to be a natural thing,” she added. “I want the surprise.”

Gwyneth Paltrow, a close friend of Ms. McCartney, was a front-row guest at the pret-a-porter show with her own daughter, 4-month-old Apple. The actress wore a pair of tweed cropped trousers from the designer’s current autumn/winter collection.

Ms. McCartney probably had im pending motherhood in mind as she designed the collection. It featured billowing drawstring smocks in white cotton voile and A-line tunics in pale turquoise chiffon strewn with silver sequins, all perfect for flattering a bump. The look was intended to bring a tropical holiday feel to the urban environment, Ms. McCartney said.

Long shift dresses with drawstring waists in pastel lace and muslin had the romantic appeal of Victorian nightdresses.

The whole feel was light and airy. Loose shirts drooping off the shoulders were worn under full, lightweight anoraks with drawstring details. Tunics with rolled-up sleeves came with slouchy cropped trousers gathered at the hem in a beige-and-cream batik print or soft shades of peach and terracotta.

However, the brief bikinis and one-piece swimsuits with plunge fronts and cut-outs were designed purely for the trim, taut tummy.