Rosie O'Donnell is known for cracking jokes, but the latest turn of events in her life is no laughing matter.

The funny lady, 50, announced on her blog Friday that her fiancée Michelle Rounds has been diagnosed with a rare disease.

"Again and again, her pain grew worse," O'Donnell writes. "It seemed impossible. No one knew what was wrong. Life changes in an instant."

The couple went through a "maze of medical mystery," according to the blog post, until Rounds was eventually diagnosed with desmoid tumors. O'Donnell calls it a "beyond rare" disease that isn't cancer but "acts cancerous" and only affects three out of every million people.

"She is recovering from surgery [she had] in June," O'Donnell reveals. "[She's] getting stronger every day. We have joined the fight against this disease, raising money and awareness."

Rounds's illness has put a damper on upcoming nuptials for the couple, who in December publicly announced their plans to marry.

"We had to postpone our wedding scheduled for next summer," O'Donnell says. In lieu of gifts for their eventual union, the couple is asking for donations to the Desmoid Tumor Research Foundation.