A 54-year-old woman had nephrotic syndrome in 2016, where an initial kidney biopsy showed podocyte disease. In 2020, a relapse with positive anti-PLA2R antibodies led to a second biopsy, which diagnosed stage II idiopathic membranous nephropathy (IMN). In 2024, facial edema and erythema appeared, serology revealed new positive ANA and anti-dsDNA antibodies along with persistent positive anti-PLA2R, fulfilling criteria for systemic lupus erythematosus (SLE). A third biopsy confirmed lupus nephritis (LN) class V. After treatment with methylprednisolone, hydroxychloroquine, and rituximab, she achieved clinical remission with obinutuzumab. Anti-PLA2R positivity is considered a specific marker of IMN, but its presence in class V LN is rare and does not exclude secondary membranous nephropathy. In patients with IMN and an atypical course, long-term antibody monitoring and repeated kidney biopsy are recommended.