The former X-Factor judge began her caption by writing: “Spot the difference”, before announcing the newest member of her family.
“On this Valentine’s day, we would like to celebrate love in the most awesome way... Beau Benedict Enthoven Williams,” she wrote in reference to her newborn.
“As with Coco, he is biologically ours, but born via the same incredible surrogate.”
In addition to Beau, Williams and Field have three children together: seven-year-old Theodora Rose, five-year-old Charlton Valentine and one-year-old Colette Josephine.
Colette “Coco” Josephine was born in September 2018, also via surrogate.
In her new Instagram post, Field expressed her joy over welcoming Beau to the Williams clan.
“We are so blessed to have our healthy son safely in our arms and are officially complete as a family,” she wrote, signing off her message: “The Williams Family.”
Several Instagram users congratulated the celebrity couple on their new arrival.
“Wow, wow, wow, so happy for you both,” commented Loose Women panellist Saira Khan. “Congratulations.”
“Amazing the best news ever,” stylist Karl Willett said.
In 2018, Williams and Field both served as judges on The X-Factor alongside Simon Cowell and former One Direction band member Louis Tomlinson.
In April 2019, the couple announced that they had decided to exit the show.
“We’re gutted to tell you we won’t be able to return to The X Factor this year,” Williams wrote on Instagram.
“We will, however, be working on projects with Simon going forward – and as huge fans of the show, we will still be tuning into The X Factor, voting and winding Simon up.”