Questions & Answers about Meine Freundin kommt heute später.
Freundin is grammatically feminine in German (the article is die Freundin).
Possessive words like mein behave like articles and change their ending according to gender and case:
- masculine / neuter nominative singular: mein Freund, mein Auto
- feminine nominative singular: meine Freundin
In this sentence, Freundin is:
- feminine
- singular
- nominative (it’s the subject)
So you must use meine, not mein.
Meine Freundin is in the nominative case because it is the subject of the sentence — the person doing the action.
- Wer kommt heute später? – Meine Freundin.
(Who is coming later today? – My girlfriend / female friend.)
Subjects in German normally take the nominative case, so you use the nominative form of the possessive: meine.