Assessing patient frailty during triage evaluations has become increasingly relevant in Emergency Departments (ED). This study aimed to externally validating the Triage Frailty and Comorbidity (TFC) tool. This prospective study was conducted from June 1 to December 31, 2023. During this period, 12 triage nurses applied the TFC tool during triage evaluation of ED patients. We used receiver operating characteristic (ROC) curves and Decision Curve Analysis to assess the predictive ability of the TFC tool for a 90-day mortality (the same endpoint used during tool development) and a 30-day mortality. 1270 patients were included and 56 of them died within 90 days. The TFC tool had an AUROC of 0.894 (0.858-0.929) for 90-day mortality and 0.885 (0.834-0.938) for 30-day mortality. In Decision Curve Analysis, it yielded higher net benefits up to a threshold probability of 0.30. The externally validated TFC tool appears very effective at identifying patients with increased risk of 90-day mortality after ED attendance. It could be implemented in clinical practice and enhance the predictive ability of standard triage systems.