Over on Instagram, the BBC star, 46, shared a precious snapshot of her little ones enjoying a tender embrace ahead of Kit's "new chapter" at school.
Kit, four, was pictured looking smart in his brand-new blue school uniform. Prepped for his big day, the youngster could be seen wearing a bright blue rucksack equipped with a matching blue water bottle.
He looked so sweet in the image as he sweetly hugged his little sister Annie who stood next to her big brother wearing a simple white T-shirt and a pair of colourful leggings.
Alongside her photo, a proud Alex penned: "He was amazing. A kiss goodbye and off he went. Excited about this new chapter and who can ask for more."
Detailing her rollercoaster of emotions, the former Strictly contestant continued: "Me, I didn't handle it with quite as much poise. So proud of this tenacious little boy but I'll miss our mornings."
Fans and friends were quick to send their support, with one follower sympathising: "I feel your pain, it's so hard," while another wrote: "Such a gorgeous photo! Good luck to him. Often so much harder for the mummy's."
A third remarked: "Oh it's so bitter sweet isn’t it?! Letting them fly is heartbreaking for us mums [red heart emoji] sending a lot of love," and a fourth agreed: "That takes me back. It's not easy letting them go and I'm not sure it gets any easier, just different. Be easy on yourself."
Alex shares Kit, Annie and six-year-old Teddy with her husband Charlie Thomson. Since welcoming her brood, the TV star has been incredibly open and honest about the realities of juggling a career with parenthood.
In conversation with Good Housekeeping, the mother-of-three said: "For me, personally, some days I don't think it's possible. It's a struggle.
"I try to be the best mother I can be, but some days I'm absolutely awful at it. Life isn't a series of perfect days where work is going amazingly, and you're a brilliant wife… That's how it is for everybody I think, but people are just too scared to say it."
Whilst the couple relish spending time with their adorable brood, it seems like Alex and Charlie have officially ruled out the possibility of welcoming a fourth child.
Speaking exclusively to HELLO! magazine in 2021, the brunette beauty explained: "No, this is it. Even the grandparents went, 'Oh my gosh, we're really excited but this is it then, isn't it? This is it.'
Musing on her third pregnancy, she went on to say: "It's that classic thing of, we met a little bit later than I bargained for than when I was in my early twenties. I just thought I've been really lucky to have two healthy boys - fantastic, that's our unit.
"And I suppose I always thought, had we started sooner, three would have been lovely. But I never thought it was going to be an option for us. So yeah, it's really special."