Katie Thurston has been diagnosed with breast cancer

She wrote on Instagram: "Life update: I have breast cancer.

"Yesterday I saw all the couples post their Valentine's Day celebrations. I felt envious if I'm being honest. Jeff took me to Hawaii and after, we were going to travel the world before planting roots together in NYC finally. But instead, my Vday was spent coordinating a place to live as I have to go back to LA for more testing and treatment.

"I used my morning to figure out insurance for NYC and laws on preexisting conditions. I scheduled appointments for another biopsy, fertility, mental health, surgery, as well as meeting with my team to discuss the overall treatment plan, which will include chemo."

The former 'Bachelorette' star went through a "range of emotions" in the weeks leading up to her diagnosis, but now wants to use her platform to help raise awareness of breast cancer and is ready to "fight" the disease.

She added: "I experienced a range of emotions over the past two weeks. Despair. Anger. Sadness. Denial. And then strength. Purposeful. Ready. I cried a lot. I tried to even make a video instead of this post and couldn't.

"But one thing I did early on was search other stories like mine. Other young women with breast cancer. Invasive ductal carcinoma. Mastectomy.

"Pregnancy after breast cancer. All of their stories helped. So I intend to be the same for others.

"This is day one of sharing and is going to be a long one. This first step of acceptance of my reality was the hardest. But I am ready to fight this."

Katie concluded her message by thanking her husband-to-be for his constant support and admitted that she has no idea how she would cope without him.

She said: "And I saved the best for last. To my extraordinary husband to be @jarcuri - I don't know how I'd do this without you. The selfless love that you smother me in is beyond anything I imagined I'd be blessed with. I love you to the fullest in this lifetime and the next."