Learn Hardcore Russian: Мне было грустно, хотя конец фильма был замечательным. - I felt sad, although the ending of the movie was wonderful.

Я был грустный is grammatically possible, but it’s less neutral. It sounds more like “I was a sad person / looked sad” (describing you as having the quality of being sad), whereas мне было грустно is about your inner feeling at that moment, which is what we usually want here.

Why is мне in the dative case?

In Russian, the dative is often used for the experiencer of a feeling or state in impersonal sentences. The structure is basically:

Dative (person) + быть (to be) + word for the state

Examples:

Мне весело. – I’m having fun.
Ей было скучно. – She was bored.
Им будет трудно. – It will be hard for them.

So мне = “to me”, marking you as the person who experiences the sadness.

Why is the verb было in the neuter form?

In мне было грустно, the sentence is impersonal—there is no real grammatical “I” as the subject. Instead, the state itself (being sad) is what exists.

In such impersonal constructions in the past, Russian usually uses neuter singular:

Мне было холодно.
Ему было стыдно.
Нам было весело.

Think of было here as something like English “it was” in “It was cold,” but in Russian the “it” is not an explicit pronoun, so only the neuter verb form remains.

What exactly is грустно here — an adverb or an adjective?

Formally it looks like an adverb, but in Russian grammar грустно in this kind of sentence is called a predicative or a category-of-state word. It’s used specifically in the predicate (the part of the sentence that says what the state is):

Мне грустно.
Ему страшно.
Здесь темно.

You wouldn’t normally use грустно to modify a noun (“a sad boy”); for that you’d use грустный мальчик. So:

мне грустно – I feel sad
грустный фильм – a sad film

What’s the difference between грустно and грустный?

грустно – used to describe a state or mood (usually in impersonal or predicative constructions):
- Мне грустно. – I feel sad.
- Здесь грустно. – It feels sad here.
грустный – a regular adjective describing a noun:
- грустный фильм – a sad film
- грустный человек – a sad person
- я был грустный – I was (a) sad (person / in a sad state).

In the sentence Мне было грустно, we’re talking about your temporary emotional state, so грустно is the natural choice.

Why is there a comma before хотя?

Хотя introduces a subordinate clause that expresses contrast (“although”, “even though”). In Russian, subordinate clauses are normally separated from the main clause by a comma.

Structure here:

Main clause: Мне было грустно – I felt sad
Subordinate clause with хотя: хотя конец фильма был замечательным – although the ending of the film was wonderful

Hence the comma:
Мне было грустно, хотя конец фильма был замечательным.

What is the function of хотя here? Could we use но instead?

Хотя means “although / even though” and introduces a subordinate clause. It puts the “positive” fact in the background and emphasizes the contrast with the main statement:

Мне было грустно, хотя конец фильма был замечательным.
→ I felt sad, although the ending was wonderful.

Но means “but” and connects two main clauses:

Конец фильма был замечательным, но мне было грустно.
→ The ending was wonderful, but I felt sad.

The meaning is similar, but:

хотя = “despite the fact that…”, used in a subordinate clause
но = “but”, coordinating two main clauses

Both are correct, just a slightly different structure and emphasis.

Why is it конец фильма, with фильма in the genitive case?

In Russian, конец (“end”) usually takes genitive to show what something is the end of:

конец фильма – the end of the film
конец дня – the end of the day
конец истории – the end of the story

The pattern is:

конец + genitive (чего?)

So фильма is the genitive singular of фильм.

Why is замечательным in the instrumental case?

In конец фильма был замечательным, the adjective замечательный (“wonderful”) is used as a predicative (part of the compound predicate). In such cases, Russian often uses the instrumental case:

Он был врачом. – He was a doctor.
Книга была интересной. – The book was interesting.
Конец фильма был замечательным. – The ending of the film was wonderful.

You could also say:

Конец фильма был замечательный.

Both замечательный (nominative) and замечательным (instrumental) are grammatically correct. The instrumental can add a slight nuance of evaluation or characterization, sometimes felt as a bit more “bookish” or descriptive, but in everyday speech they’re very close in meaning.

Could we say Мне стало грустно instead of Мне было грустно? What’s the difference?

Yes, both are correct, but they’re not the same:

Мне было грустно. – I was sad / I felt sad.
Describes your state over a period of time in the past.
Мне стало грустно. – I became sad / I started to feel sad.
Focuses on the moment the feeling appeared (a change of state).

In the original sentence, Мне было грустно, хотя конец фильма был замечательным, the speaker is describing how they felt during or after the film, so было is appropriate. If we say стало, we highlight the moment when the sadness began, for example at the ending.