Catherine, Princess of Wales says she has completed her chemotherapy treatment after being diagnosed with an unspecified form of cancer following abdominal surgery. “As summer draws to a close, I cannot tell you what a relief it is to have finally completed my chemotherapy treatment,” the Queen says in a new YouTube video posted by the Prince and Princess of Wales’ account.

In the video – which was filmed in Norfolk, England, last month, a Kensington Palace spokesperson told Sky News – Kate, 42, is seen enjoying the scenery with her husband Prince William and their three children, Prince George, Princess Charlotte and Prince Louis. She also opens up about her thoughts on battling cancer.

“The last nine months have been incredibly tough for us as a family,” says Kate, who publicly announced her cancer diagnosis in March. “Life as you know it can change in an instant and we’ve had to find a way to navigate the stormy waters and the unknown path.”

“Cancer is complex, scary and unpredictable for anyone, especially those closest to you. With humility, you also confront your own vulnerabilities in ways you’ve never considered before, and you gain a new perspective on everything. Above all, this time has reminded William and me to reflect on and be grateful for the simple but important things in life that so many of us often take for granted. Simply to love and be loved.”

The princess then revealed some details about what her life will be like now that she no longer has to undergo the treatment that had largely kept her from her official royal duties.

“My focus now is to do everything I can to stay cancer-free,” she says. “Although I have completed chemotherapy, my road to healing and full recovery is long and I must continue to take each day as it comes. However, I am looking forward to getting back to work and doing a few more public engagements in the coming months when I can.”

“Despite everything that has happened before, I begin this new phase of recovery with a renewed sense of hope and appreciation for life,” she continues. “William and I are so grateful for the support we have received and have drawn much strength from all those helping us during this time. The kindness, compassion and empathy of everyone has truly impressed us. To everyone continuing their own cancer journey – I stand with you, side by side, hand in hand. Out of the darkness can come light, so let that light shine brightly.”

This is the first health update since Kate shared in June that she was “not out of the woods yet” and would remain in cancer treatment for several more months. “I’m making good progress but as anyone going through chemo knows, there are good days and bad days,” the royal wrote in an Instagram post on June 14, just before attending the Trooping the Colour event that month. “On those bad days you feel weak, tired and need to give your body some rest. But on the good days, when you feel stronger, you want to make the most of feeling good.”

“On the days when I feel good enough, it’s a joy to get involved in school life, spend my free time doing things that give me energy and positivity, and also work a little from home,” she added. “I’m learning to be patient, especially with uncertainty. I take each day as it comes, listen to my body and give myself the much-needed time to heal.”

In March, it was revealed that the princess had undergone major abdominal surgery in London, which was deemed successful. “However, tests after the operation showed that cancer was present, so my medical team advised me to undergo preventative chemotherapy and I am now in the early stages of that treatment,” she said in a video message.

Here you can find out everything you need to know about preventive chemotherapy.

What is preventive chemotherapy?

“Preventive chemotherapy is not a technical term, it’s a layman’s term. It’s more like adjuvant treatment, meaning ‘in addition,'” Ginger Gardner, MD, a gynecologic oncologist at Memorial Sloan Kettering Cancer Center and chair of the Foundation for Women’s Cancer, tells Yahoo Life. “This general term could be applied to a situation where a tumor has been removed and (doctors) still want to provide treatment coverage” to prevent cancer from coming back. It could also be used to prevent recurrence after a tumor has been destroyed by radiation therapy.

When someone is prescribed preventive chemotherapy, it usually indicates that no visible cancer remains after surgical removal or radiation treatment, and there is no evidence that the tumor has spread to other parts of the body—in other words, that the cancer has not metastasized.

But even when a cancerous tumor is completely removed or destroyed, cancer cells can break away from primary tumors and travel to other parts of the body. Cells that are too small for doctors to see may still remain. Preventive chemotherapy – which can be given as pills or intravenously – could be used to “reduce the risk of microscopic cells coming back or delay their chance to do so,” Gardner says.

While chemotherapy is not the only way to achieve this, it is one of the most effective and widely used. Other preventative treatments include hormone therapies, which can cut off the energy supply to tumors that are driven by hormones (such as certain types of breast cancer), radiation therapy, immunotherapy, and targeted therapies that block non-hormonal cancer drivers.

What are the side effects of preventive chemotherapy?

Preventive chemotherapy does not necessarily involve a lower dose than a typical treatment for existing cancer, so the potential side effects are the same, although they vary depending on the specific type of cancer being treated and the drug being used. In general, the following side effects may occur:

How long does preventive chemotherapy need to be administered?

According to the Mayo Clinic, treatment can last as little as a few weeks or as long as 10 years. However, Gardner adds, “cancer is not just one disease,” which means the type, duration and dose of chemotherapy are carefully chosen based on the type of cancer, its stage and biology, and what is best for the patient’s quality of life.

Whether and for how long someone undergoes preventative chemotherapy, and how effective the therapy will be, depends on the type of cancer being treated. The treatment has been shown to be effective in preventing recurrences in both breast and colon cancer, for example. Kate said in March she was in the “early stages” of treatment.

The effectiveness of chemotherapy in this way also depends on the stage of the cancer, whether the disease is hormone-dependent, and whether it has spread to lymph nodes. In some cases and for certain types of cancer, doctors advise against preventive chemotherapy altogether.

“If adjuvant therapy provides sufficient benefit to maintain a durable remission, then some side effects are acceptable,” says Gardner. “However, if the biology of the disease means that someone is not going to benefit from this type of therapy, then it is not worth it and we make decisions about adjuvant treatment based on that trade-off.”

In the case of the Princess of Wales, “whatever it is, the fact that she has taken proactive measures against a seemingly harmless disease and that she has, by her own account, overcome the disease, is taking proactive steps (to prevent a recurrence) and is considering her children is important,” Gardner says.