The 25-year-old model struck up a friendship with the blonde beauty almost straight away and believes the fact they were both born on August 3 ensured that they got on like a house on fire immediately.
The brunette beauty explained: ''Karlie and I bonded straight away. Once we found out we had the same birthday, we were like, 'OK, this was destined to be!' It's difficult now because we're both so busy and we don't do as many shows. But I was with her last night and every time we do get together it's as though we haven't been apart. I love her dearly - she's like a little sister.''
And Karlie, 23, isn't the only fellow supermodel that Jourdan views as a sibling as she also shares a similar bond with Cara Delevingne.
She told the Telegraph magazine: ''Cara, I also consider a sister. I was so heartbroken when she told me she was going to focus on acting and stop modelling. I said, 'No, my partner in crime!' But I'm so happy for her because this is what she really wants. She's in a great place and I love seeing her smile, love seeing her happy... I just miss being backstage with her. It didn't seem to be work. It was easy, just chilling with a friend and then doing a show. When you're away from your family, with long days of fittings and castings, she had a great, positive energy to be around.''