After a terminal brain cancer diagnosis, a mother is facing the inevitable heartbreak of leaving her two sons to grow up without her.

When Sara Chivers, 34, found out her longtime battle with cancer had become terminal, she decided to write an emotional goodbye letter to her beloved children, The New Daily reports.

The Australian native was given the devastating news back in March, when doctors told her the three tumors in her brain were inoperable. She had previously beat the same disease in 2008.

In her letter, she touched upon many topics, sharing words of wisdom, giving sound advice, and speaking of her unconditional love for her sons, 3-year-old Hugh and Alfie,18 months.

"Be brave in your convictions and believe in yourself. Never tease or ridicule someone because they're different to you. You will be a better person by surrounding yourself with people who will challenge your views and beliefs," the letter said.

"Love hard. As they say, it is better to have loved and lost, than never to have loved at all. That's how I feel about you both," she wrote. "Heartbroken doesn't come close to describing the pain I feel at not being in your lives in the future, but I would never change or forego the time we have spent together and the immense joy you have brought me. You are without a doubt my proudest accomplishments."

She also spoke of the strength of her husband: "Your Dad is the most admirable, courageous man I have ever known. He is my companion, my rock, my everything. He has shown true grit in the face of our adversities, and without him beside me I would have crumbled."

However, in a devastating twist, the couple have recently found out their youngest son has also been diagnosed with brain cancer as well.

In October, Sara and her husband Leigh learned Alfie was also diagnosed with brain cancer, albeit a different kind. The couple had originally believed he had a teething infection, which sadly instead turned out to be a tumor the size of a pear.

"We were in a state of disbelief," Sara told PEOPLE when she found out about Alfie's condition. "It wasn't even on the scale of our worst fears; it was an inconceivable situation."

Sara's brain cancer is called glioma, while her son's is atypical teratoid rhabdoid. There is a one in three million chance of getting this type of disease.

The chances of a mother and son having brain cancer is extremely rare, her neurosurgeon Bandu Kavar said. He compared it to a case of lighting striking twice, adding it is more likely for someone to win the powerball.

While a parent's worst nightmare, the diagnosis has given Sara another reason to continue fighting her battle against her cancer. She refuses to allow her son to become another statistic, adding: "It's not about me any more. It's about him."

According to the ABC News, In the past 30 years, brain cancer mortality rates have only improved by 1%, compared to the mortality rates of all other cancers has been improved by 20%.  

"To think that he has to go through this journey, at 18 months old," Sara said. "It's been so, so hard to see him go through that."

Sara is desperately trying to save her son from suffering the same fate as her. Since Alfie's diagnosis, Sara has since had three operations to remove as much of his tumor as possible, and reduce the fluid in his brain.

Sara's sister Stephanie has started a GoFundMe page to help relieve the family of some costs.