What is the subject here and what the object?
I think the subject is fy atgoffa "my reminding", the verb is bydd rhaid "will be necessary", and there is a prepositional phrase i ti "to you".
Oh, it's the preposition "i"! I suppose this shows me the benefit of pronouns having a separate subject and object form. I thought "i ti" was a subject and object, but I just couldn't figure out which was which or where "fy atgoffa" fit in.