The TV chef and his wife of 16 years looked over the moon as they revealed their big baby news at Thursday's event. Jools wore a metallic jacket and a black jumpsuit, accentuating her growing bump.
Jools and Jamie are expecting their fifth child
The 41-year-old mum is said to be thrilled at the news, "Jools is radiant and blooming for the fifth time. The baby is expected in August," a source told The Daily Mail.
The happy couple, who married in July 2000 after dating for seven years, are parents to daughters Poppy Honey Rosie, 14, Daisy Boo Pamela, 12, Petal Blossom Rainbow, six, and five-year-old son Buddy Bear Maurice.
Last year, the mother-of-four hinted that she would like to have another baby with her celebrity chef husband.
The happy couple announced the news on Thursday
"There's this Moses basket I designed," she said in an interview with Style. "I haven't been able to test personally yet. It would be nice to put it to use."
Jools, whose Twitter biography simply describes her as "a mum", has made no secret of her desire to have another child, In 2012, she told Red magazine: "I want a fifth," she said.
"But I know it would be wrong. I never get any time to spend with Jamie as it is. He has said give it a couple of years, then maybe we can think about it."
The pair married in 2000
Jamie, who rose to fame in 1999 at the age of 24, has also mentioned his wife's plans to expand their family. "I took her out and she goes, 'OK are we going to have another kid then?' I said, 'You what?'" he said. "The woman wants another baby. So watch this space. But with all the power in my body we are not having another baby."
The doting parents, who first started dating when they were 18, married at the All Saints Church in the groom's home village of Rickling, Essex. At the time they were both 25 and had known each other for more than ten years.
The couple welcomed their first child Poppy Honey in 2002, followed by Daisy Boo 13 months later. Jamie and Jools became parents for a third time when little Petal Blossom was born in 2009, followed by a son Buddy Bear 17 months later.