Cutibacterium acnes is a low-virulence pathogen that can cause prosthetic valve endocarditis (PVE), presenting significant diagnostic challenges due to its slow growth and indolent clinical course. We report a case of a 57-year-old male with a history of tissue aortic valve replacement, who presented with 6 months of intermittent fever and a nonproductive cough. Initial tests showed elevated inflammatory markers and moderate aortic regurgitation, but no vegetations were identified on transthoracic or transoesophageal echocardiography. After 13 months of symptoms, a PET scan showed significant FDG uptake around the bioprosthetic valve, and a single blood culture grew C. acnes. Transoesophageal echocardiography revealed abnormal rocking motion of the valve and severe paravalvular regurgitation, suggesting near-complete valve dehiscence. The patient underwent redo surgery for aortic root and valve replacement, and intraoperative cultures confirmed C. acnes infection. This case highlights the importance of considering low-virulence pathogens like C. acnes in patients with prolonged, nonspecific symptoms and initially negative cultures. Advanced imaging, particularly PET/CT, is crucial for early diagnosis and intervention. Early recognition and appropriate treatment are vital for preventing severe complications such as valve dehiscence and tissue destruction.