Earthquake forecasting is a challenging goal for seismologists and geophysicists due to the complex nature of the earthquake phenomenon. Delivering reliable forecasts is crucial for public safety. This study derives the probability of extreme events in any seismic cluster generated by the Epidemic Type Aftershock Sequence (ETAS) model. This probability is obtained as a function of time, space and magnitude. The results contribute to understanding the distinguishing features between mainshocks and foreshocks and provide insights into earthquake prediction and the probability assessment of extreme events within seismic clusters.