The 44-year-old, who gave birth to her second child on 21 January, shared a black and white shot of her holding her son while her husband kisses his head.
“Monty is two weeks old today,” Horner captioned the shot, shared on Sunday 5 February.
Horner’s fans were excited to see the first photo of baby Monty, having only previously seen a photo of his feet.
“Oh my goodness, he’s absolutely adorable,” one person wrote. “This picture is so sweet, I love it. God bless you guys.”
Another commented: “Lovely family, gorgeous photo and genuine love. You look fabulous and, more importantly, so incredibly happy. Congratulations.”
One person wrote: “Oh gosh Geri I’m just out of words... Such a beautiful, beautiful picture and your little bundle of joy how gorgeous is Monty.
“I’m so happy for you and your family bless you.”
Christian is also dad to three-year-old Olivia from a previous relationship.
Horner, who is also mum to 10-year-old Bluebell Madonna from a previous relationship, shared the news of her son’s birth on 21 January.
“Montague George Hector Horner arrived this morning, a beautiful little brother for Bluebell and Olivia #amazing-day #grateful #monty,” she wrote.
She announced she was expecting her second child in October 2016.
“The couple is overjoyed with the good news and cannot wait to welcome the newest addition to their family,” a statement for the couple read at the time.