Mrs Laycock, 34, finally gave birth to tiny Lewis after her husband John quit his job as a chef after 20 years.
After nine girls in a row, the couple had resigned themselves to being a totally female household.
But as soon as John, 37, retired after two decades in hot kitchens, delighted Mrs Laycock fell pregnant with a boy.
"I'm so excited to have a boy at last," said Sally, who has been pregnant for ten of the last 17 years."
She said that she had been told that the hot conditions in which Mr Laycock used to work could have been to blame for the couple's failure to give birth to a boy.
However, she did not believe temperature had played a part until he gave up work and she became pregnant with a boy.
Mr Laycock, of Welwyn Garden City, Herts, said: "I had to give up my job because I had two heart attacks in the space of six months and couldn't work.
"It was a hard time for us, as we're such a big family.
"But it's finally brought us a boy. We're all so excited."
The family of 12 are having an extra-special Christmas to celebrate, despite the worry of having another hungry mouth to feed.
Family and friends are buying plenty of boy's toys as presents after years of stocking up on dolls, clothes and make-up.
Baby Lewis was born a healthy 7lb 12oz on December 9.
The family are coming to terms with having a boy in the already busy household.
Mr Laycock said: "We've got a bit of planning to do because we've only got four bedrooms.
"Now we have a boy it's going to be difficult.
"I've even started building a shed in the garden to make extra space for the older girls."
The couple cope with their brood, aged two to 17, by running a military like operation each morning and bedtime, with the oldest girls helping the younger ones.
Each week they run up a £200 shopping bill and get through two loaves of bread just for breakfast.