Kim Kardashian West with her daughter North and son Saint. Picture: Instagram

Kim Kardashian West's surrogate didn't know the baby she was carrying belonged to the star, as the process was anonymous at first.

The 37-year-old reality star is expecting her third child with her husband Kanye West via a surrogate mother, and she has now revealed the woman carrying her baby didn't know to begin with that she was going to give birth to Kim and Kanye's child.

Kim - who already has four-year-old North and 23-month-old Saint with her spouse - said: "She didn't know at the beginning. She didn't know. You could do it totally anonymously. You could go that route. And I just felt like, whoever is carrying my baby, what if they weren't a fan of me or my husband? What if they didn't want to be carrying our baby? I wanted to give them that choice, and be proud and on the same page. I wanted a relationship with her."

The 'Keeping Up with the Kardashians' star insists the mystery woman was "really excited" when she eventually discovered who the parents of the tot would be.

Speaking during an appearance on 'The Real', she said: "She was really excited. She was someone who had watched the show - not like a super fan, that it would have been uncomfortable - but she'd seen my struggle and seen how open I was about it, so she was really proud to do it."

Previously, Kim said she believes she chose the "perfect" woman to be her surrogate mother, as she has the "best relationship" with her.

She said: "I love her. I have the best relationship with my surrogate. She's so nice. She is the perfect person to do this for my family. She's great. She's been amazing."

Despite being pleased with her choice of surrogate, Kim revealed she is finding the process "so much harder" than being pregnant herself, as she is struggling with the lack of control she has over her unborn tot.

She said recently: "You know, it is really different. Anyone that says or thinks it is just the easy way out is just completely wrong. I think it is so much harder to go through it this way, because you are not really in control. 

"And, you know, obviously you pick someone that you completely trust and that you have a good bond and relationship with, but it is still ... knowing that I was able to carry my first two babies and not, you know, my baby now, it's hard for me. So, it's definitely a harder experience than I anticipated just in the control area."