Australian mother of two shares heartbreaking story behind this photo: 'How can you not feel the cancer?'

Kirstin Pretorius was on vacation with her family when she took a cute photo with her husband Maurice. The Australian couple, who have two children, look as happy as can be. When you think of a picture-perfect couple ... it's Kirstin and Maurice.

But everything is not really as perfect as it seems -- beneath Kirstin's bright blonde hair and sun-kissed complexion was a woman who was actually really sick. Just weeks later, doctors discovered a lump. Kirstin had breast cancer and she had no idea.

"I look at this picture ... and all I can think is 'KIRSTIN how can you not know that there are 3 tumors thriving away in your breast? How can you not FEEL the cancer slipping into your lymph nodes?" the 34-year-old wrote in an Instagram that was posted in July but just recently started gaining attention. "'Why don't you FEEL sick? How can you be so stupid!?' But I didn't know and I didn't feel."

Since her diagnosis, Kristin has made several changes to her lifestyle, including going on a "virtually-vegan" diet and regularly exercising.

"If my doctor hadn't examined me, I'd still be blissfully unaware. I'd be packing my little plastic-free super food lunches for my girls, lecturing them on healthy lifestyles. I'd be chemically-free cleaning my home wondering why the whole world doesn't use essential oils. All the while growing and feeding my precious cancer."

She ended her post with an important message for women everywhere: "Check your boobs. Know your body. Cancer happens. To anyone."

In Australian blog Honey Nine, Kirstin has opened up about her scary journey, revealing that she was "horrified" when she first found out that she had cancer.

"I'm one of those people who always thinks everything will be fine. Even waiting for the biopsy results I kept telling myself, 'I'm sure they're going to say it was a false alarm.' So when they said, 'It's cancer,' I was shocked, I was horrified."

Though Kirstin is facing the ultimate battle of her life, she has the support of her friends and family around her.

"My mum flew out from South Africa and my sister came from Italy," Kirstin said. Her neighbors and friends in a suburb of Sydney have also offered their help.

"The community are really willing to help, and that's one of the best lessons that I've learned," she continued. "When bad things happen like this, people rally together. They're there for you, even people you don't know well. So that's one beautiful side of cancer, to see the kindness of humanity."