EWTN Catholic Q&A

Unremembered sins
Question from S.A. on 01-09-2013:

If I suddenly remembered a past sin that I wasn't able to confess (because I unintentionally forgot to), do I still need to confess it in my next confession?

Answer by Catholic Answers on 01-09-2013:

S.A.--

If the sin was a mortal sin, yes.