egg laying cocatiel

by Rose
(NSW)

I have a female cocatiel that has layed 4 eggs in 4 days.She is my only bird but a few weeks back I minded my friends male cocatiel.So not sure if the eggs are fertile.How do you know and how long will it take before we know if we are going to have little babies.Hope some one can anwser my question.Thankyou have a great weekend.