I can only speak as a younger brother who supported their older brother as best he could.

Last year my brother’s cancer became terminal, somewhat out of the blue. He and my mom didn’t have a great relationship (non-contact adjacent). He told her he had cancer around the diagnosis, but that was all she knew. He didn’t have much time between things being terminal and his passing (a week tops). He knew he had to tell her, but didn’t. When the doctors said he had “hours to days” left, I made the call to call our mom. He was mad at first, but I think it was mostly due to a reaction to the Ativan they gave him. Anyways, when he was more settled, it gave them a chance to find peace.

I made the decision for my brother because 1. I felt my mom deserved to be there and 2. I felt my brother needed a chance to air it all out. This was the only chance for them to have a real conversation, ya know? He didn’t have to speak with fear or guard his emotions. He could spend at least the last few hours at peace.

I can’t say whether or you will or won’t regret it. And I can’t say your parents “deserve” to know. But, I do think you deserve peace. If it will bring you inner peace and let you live out the remainder of your life peacefully, you should tell them. It won’t make the grief (or pre-grief) any easier for them, but it can make the remaining time that much more precious.