Öfke geçince onun aslında yorgun olduğunu anladım.

Geçince comes from the verb geçmek and the suffix -ince / -ınca, which often means when, once, or after.

So:

• geçmek = to pass
• geçince = when it passed / once it passed

In this sentence, Öfke geçince means something like when the anger passed or once the anger subsided.

Here geçmek is being used in the sense of a feeling fading away, which is very common in Turkish:

• Ağrı geçti = The pain went away
• Sinirim geçti = My anger passed

Both are possible, but -ince is shorter and very natural in everyday Turkish.

Compare:

• Öfke geçince = when the anger passed / once the anger passed
• Öfke geçtikten sonra = after the anger had passed

The second version is a bit more explicit and slightly heavier. The -ince form is very commonly used for this kind of time relationship.

The sentence does not explicitly say whose anger it is.

That is normal in Turkish. If the context already makes it clear, Turkish often leaves that kind of information unstated.

So Öfke geçince just means when the anger passed. Depending on the wider context, that could mean:

• the speaker’s anger
• the other person’s anger
• the general anger in the situation

Turkish often relies on context more than English does.

Onun is the genitive form of o, so it can mean his, her, or its.

Here it marks the subject of the embedded clause:

• onun ... yorgun olduğunu = that he/she was tired

This is a very important Turkish pattern. In subordinate clauses of this kind, the subject often appears in the genitive:

• benim geldiğimi = that I came
• senin haklı olduğunu = that you are right
• onun yorgun olduğunu = that he/she is tired

So o would not work here in the same way. Onun is needed because the clause is built as a noun clause.

Yes, very often it can be omitted if the context already makes the subject clear.

So you may also hear:

• Öfke geçince aslında yorgun olduğunu anladım.

This still means I realized that he/she was actually tired, assuming the listener already knows who is being talked about.

Including onun makes the sentence clearer or more explicit.

This is one of the most important structures in Turkish.

Yorgun olduğunu means that he/she was tired.

Breakdown:

• yorgun = tired
• olduğunu = roughly that he/she was

More specifically, olduğunu comes from olmak and contains several pieces:

• ol- = be, become
• -duk / -dık / -dik / -duk type structure = used in noun clauses
• -u = third person possessive-related marking inside the clause
• -nu = accusative marking on the whole clause

You do not need to memorize every label immediately, but the key idea is this:

Turkish often expresses that... clauses by turning them into a kind of noun phrase.

So:

• yorgun olduğunu anladım = I understood / realized that he/she was tired

Because the whole clause onun aslında yorgun olduğunu is the object of anladım.

Think of it like this:

• What did I realize?
• I realized that he/she was actually tired.

In Turkish, when this kind of subordinate clause functions as a definite direct object, it usually takes the accusative.

So the ending on olduğunu helps mark the entire embedded statement as the thing that was understood.

Aslında means actually, in fact, or really.

It adds the idea that the truth was different from what it may have seemed at first. In this sentence, it suggests something like:

• maybe the person seemed rude, upset, or difficult
• but later the speaker realized the real issue was fatigue

Its position is flexible, but here it naturally modifies the embedded idea:

• onun aslında yorgun olduğunu = that he/she was actually tired

No. Turkish pronouns do not mark gender the way English does.

So onun can mean:

• his
• her
• sometimes its

Likewise, o can mean:

• he
• she
• it

You only know the gender, if relevant at all, from context.

Because Turkish normally places the main finite verb at the end of the sentence.

So the sentence is structured like this:

• Öfke geçince = time clause
• onun aslında yorgun olduğunu = object clause
• anladım = main verb, I understood / realized

This is very typical Turkish word order. English usually puts the verb earlier, but Turkish often saves the main verb for the end.

In this sentence, I realized is usually the more natural English translation.

Anlamak literally means to understand, but in many contexts it also means to realize, especially when someone comes to understand something after a change in perspective or after new evidence appears.

So here:

• anladım = I realized

That sounds especially natural because the speaker only came to this understanding after the anger passed.