Prince William is opening up about a dark time in his past.

In the trailer for the upcoming episode of Apple TV+’s "The Reluctant Traveler with Eugene Levy," the Prince of Wales got candid about the cancer diagnoses that rocked his family.

"We’ve been very lucky. We hadn’t had many illnesses in the family for a very long time. My grandparents lived until they were in the high nineties," Prince William said in the clip, referring to the late Prince Philip and Queen Elizabeth.

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"They were the vision of fitness, and stoicism, and resilience, if you like. So we’ve been very lucky as a family," he continued. "But I think, when you suddenly realize that the rug, if you were, the metaphorical rug, can be pulled from under your feet quite quick at any point."

"You maybe think to yourself, 'It won’t happen to us, we’ll be OK.' Because I think everyone has a positive outlook, you’ve got to be positive," he added. "But when it does happen to you, then it takes you into some pretty not great places."

In February 2024, Buckingham Palace announced that William's father, King Charles III, had been diagnosed with a form of cancer and was undergoing treatment. A "separate issue of concern" was identified during the monarch's "benign prostate enlargement" procedure at the London Clinic. The king continues to undergo treatments.

One month later, William's wife, Kate Middleton, announced her own cancer diagnosis, two months after she underwent planned abdominal surgery.

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Earlier this year, the mom of three announced that her cancer was in remission.

"I wanted to take the opportunity to say thank you to The Royal Marsden for looking after me so well during the past year," she wrote on X. "My heartfelt thanks goes to all those who have quietly walked alongside William and me as we have navigated everything."

"We couldn’t have asked for more," she continued. "The care and advice we have received throughout my time as a patient has been exceptional. In my new role as Joint Patron of The Royal Marsden, my hope is, that by supporting groundbreaking research and clinical excellence, as well as promoting patient and family wellbeing, we might save many more lives, and transform the experience of all those impacted by cancer."

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"It is a relief to now be in remission and I remain focused on recovery. As anyone who has experienced a cancer diagnosis will know, it takes time to adjust to a new normal. I am however looking forward to a fulfilling year ahead. There is much to look forward to. Thank you to everyone for your continued support."

Speaking with Levy, William said those were the "hardest" times.

"I’d say ‘23-’24 was the hardest year I’ve ever had," William says in the clip. "You know, life is sent to test us and being able to overcome that is what makes us who we are."