Geri Horner had unsuccessful fertility treatment.
Geri Horner
The former Spice Girls singer was resigned to thinking she and husband Christian Horner - who each have a daughter from previous relationships - wouldn't have a child of their own together before she fell pregnant naturally with their son Monty, now nine months.
She said: "I wanted another baby and I'd tried an assisted route and it didn't work.
"I feel for any woman who has that natural biological longing, it's tough. I'd got to thinking I have a child, my husband has a daughter, and accepting this is our lot. Then Monty came naturally."
The 45-year-old singer loves seeing her 11-year-old daughter Bluebell taking care of her younger brother.
She added in an interview with Red magazine: "Bluebell is sweet with him. Helps me change his nappy, pushes the pram."
The 'Lift Me Up' singer previously battled bulimia and she's doing her best to make sure her daughter grows up body confident.
She said: "She's at an age where they're all comparing their bodies.
"I can't control that, but I can give her the facts of healthy eating, tell her diets don't work. I try to give her confidence to love her body.
"Worrying about the size of your thighs takes up so much of your twenties. It's a shame."
Geri is keen not to spoil her children and wants them to appreciate the importance of appreciating material things, even though her daughter is annoyed not to have her own mobile phone.
She said: "She's the only one not to have one in her class."
The 'Stop' hitmaker recently admitted she is very "proud" of how Bluebell has adjusted to having a new stepfather, baby brother, and four-year-old stepsister Olivia in her life after so long with it just being the two of them.
She said: "I never forced anything, I let them find their own way. She calls him Daddy and that was her choice. They have a really nice bond.
"It has all been a huge change for Bluey, after having me to herself for so long, suddenly having not just Christian in her life, but a little stepsister, who is just so sweet and now a baby brother.
"It's a lot for a young girl but she's a great kid, smart and funny with a big heart. I'm proud of her."