Carrie took to her Instagram to share a photo of herself walking hand-in-hand with her two children, Wilfred and Romy, with all three with their backs to the camera, alongside a touching photo where a child's hand was seen resting on her growing baby bump.
In her first photo, the mum-of-two wore a stylish jacket alongside a plaid skirt, while her son wore a stylish blue jumper with denim jeans and her daughter wore a cute pink jumper with a smiley face embellishing its back.
In her caption, Carrie said: "New team member arriving in just a few weeks [chick emoji]. I've felt pretty exhausted for much of the last 8 months but we can't wait to meet this little one."
She also revealed how her children were reacting to the news they were getting a younger sibling, explaining: "Wilf is v excited about being a big brother again and has been chattering about it nonstop. Don't think Romy has a clue what's coming… She soon will!"
Fans were absolutely overjoyed for the couple, as one enthused: "Oh Carrie this is such wonderful news! I'm so happy for you all! Sending you and Boris many congratulations!"
A second added: "Congratulations! Absolutely glowing," while a third commented: "I had a feeling you might be. What wonderful news. God bless x," and a fourth wrote: "BEYOND EXCITED!"
Many others shared simpler messages of congratulations and others filled the post's comments section with heart emojis.
"At the beginning of the year, I had a miscarriage which left me heartbroken," she wrote. "I feel incredibly blessed to be pregnant again but I’ve also felt like a bag of nerves. Fertility issues can be really hard for many people, particularly when on platforms like Instagram it can look like everything is only ever going well."
She added: "I found it a real comfort to hear from people who had also experienced loss so I hope that in some very small way sharing this might help others too."
From photos shared by Carrie online, her son Wilfred already appears to be following his father when it comes to the hair department. As the pair enjoyed a Winter Wonderland together, Wilfred's wild blonde locks could be seen mirroring those of his father.
Boris, meanwhile, has four grown-up children with his second wife Marina Wheeler, who the politician married 25 years ago. He also has an eleven-year-old daughter with Helen Macintyre, who is an art consultant.
During 2019 general election campaign, he was asked was asked by radio station LBC how many children he had and responded: "I love my children very much but they are not standing at this election. I'm therefore not going to comment on them."
See these sweet moments of her children's lives that Carrie has captured...
Keep up with the latest celebrity stories Sign up to our HELLO! Mail newsletter and get them delivered straight to your inbox.