The All of Me singer and Chrissy secretly spent years trying to start a family, and the model went public with their desperate desire to have children in September (15), when she admitted they had turned to medical experts for in vitro fertilisation (IVF) treatment.

The process worked, and Chrissy gave birth to daughter Luna in April (16).

Now the new mum has revealed it was Kim, who is married to John's close pal Kanye West, who actually turned them on to their fertility doctor after enduring her own pregnancy problems.

During an Insider Circle chat for Kim's app, the two women shed a little light on their long friendship, and discussed how becoming mothers had strengthened their bond.

"I think it's brought us closer," Kim said of motherhood. "Because when you're a mum and you figured it out, you want to tell all your friends."

Her comments prompted Chrissy to share how Kim had played a key role in helping her and John become parents, while also sharing other important information she had learned through the births of her three-year-old daughter North and son Saint, who was born in December (15).

"You helped us find the doctor for IVF and a lot of the same things...," she explained. "You taught me everything."

Elsewhere in the candid conversation, Chrissy confessed she and John didn't have the greatest time at Kim and Kanye's fairytale wedding in Europe in 2014 - because they were fighting.

"John and I got in the biggest fight at Kim and Kanye's wedding... that you've ever seen in your whole life," she teased, before Kim admitted she and Kanye had also fallen out on their friends' big day back in 2013.

"Wait, I got in a fight with Kanye during your wedding," the 35-year-old remembered. "I didn't go... (North) was just born and I was so fat, and I had nothing to wear so he kept texting me: 'Babe, this is the most beautiful wedding,' 'Babe, this is so pretty. I wish you were here.' Literally a play-by-play text... We got into the biggest fight. (I was like), 'Just stop texting me. Go enjoy the wedding, you're making me feel so bad!'"