Boris Johnson and Carrie arrive to attend an event. File

"New team member arriving in just a few weeks," Carrie Johnson posted on her Instagram account, alongside a photograph of her hand-in-hand with their two young children, Wilfred and Romy.

"Wilf is v excited about being a big brother again and has been chattering about it non-stop. Don't think Romy has a clue what's coming. She soon will," she added.

Wilfred was born in April 2020, not long after Johnson was treated in hospital intensive care for COVID-19. Romy then arrived in December 2021, again when Johnson was still Britain's prime minister.

He was ousted the following summer, amid a revolt within his ruling Conservatives after a series of scandals, including COVID-19 lockdown-breaking parties at Downing Street.

The 58-year-old Johnson, who remains a Tory lawmaker but is rarely seen in the House of Commons chamber, has been married three times.

He has four children from his second marriage to the lawyer Marina Wheeler, and will now have three with Carrie, 35, a former Conservative Party media adviser whom he wed two years ago.

The ex-leader has another child, a daughter, from an extra-marital affair.

In September 2021, before Romy's birth and after years of speculation about how many children he had, Johnson confirmed to US TV network NBC in an interview that at that time he had six.

Agence France-Presse