A giant cell tumor is a common, benign but locally aggressive bone tumor faced by orthopedic surgeons. The proximal humerus is a rare site of occurrence for this tumor, and the challenges posed while approaching such a case are discussed in this report of a 29-year-old male who presented with pain, swelling, and restricted motion at the left shoulder. Plain radiographs and MRI were suggestive of an aggressive giant cell tumor of the proximal humerus, which was confirmed on histopathological examination. Due to the lesion's extensive soft-tissue involvement, en-bloc resection with reconstruction was planned, but due to the COVID-19 pandemic, surgery was delayed. During the same period, the patient had trivial trauma to the same shoulder, following which the size of the lesion began increasing. The patient was operated on with en-bloc resection and reconstruction with a custom megaprosthesis; following the surgery, there was a complete resolution of pain and improvement in the range of motion. En bloc resection and replacement with a customized megaprosthesis, though technically demanding, offer a safe and cost-effective modality for limb salvage surgery for large giant cell tumors, with good functional outcomes and decreased chances of recurrence.