The 45-year-old former Spice Girl called her son a “gift”, adding that he is the “sweetest, most affectionate baby”.
Monty is Horner’s first child with her husband Christian Horner. She is also mum to 10-year-old Bluebell Madonna from a previous relationship.
“I totally understand now that protective thing mums have with their sons; that deep-rooted feeling of: ‘That’s my boy,’” she told Hello! Magazine.
When asked if she wanted to have more children with Christian, the Horner replied: “There’s room for another one, for sure, and if that happened, that would be great. But either way is okay.
“We’ve got our hands pretty full and we’re very grateful for what we have.”
Horner added that she is the happiest she has ever been, going from being a single mum to Bluebell to a “blended, modern family”.
She married Christian Horner in June 2015 and the couple welcomed their first child - Montague George Hector Horner - in January 2017.
The mum-of-two has recently spoken out about the pressure mums face to snap back into shape after having a baby.
“I think we need to take the pressure off women about how they look and bouncing back after baby weight,” she told The Mirror back in June.
“It’s not fair, and I’m questioning how helpful it is to say to women: ‘Omg you’ve just gone and snapped back’. Every single body is different.”
Read Horner’s full interview in this week’s Hello! magazine, out now.