Learn Hardcore Spanish (Latin America): El vecino al que le presté el trapeador me lo devuelve mañana. - The neighbor to whom I lent the mop will return it to me tomorrow.

Al que literally means to the one (who/that). You need the preposition a because the verb prestar takes an indirect object with a (lend something to someone). In Spanish, when a relative pronoun follows a preposition, you can’t use bare que; you must use a form like el que/la que/los que/las que or quien/quienes. Also, al is the contraction of a + el.

Why is there a le in al que le presté el trapeador? Who does it refer to?

Le is the indirect object pronoun referring to al vecino. It’s clitic doubling: Spanish typically repeats the indirect object with a pronoun even when it’s also expressed as an a + phrase. So: Le presté el trapeador al vecino = I lent the mop to the neighbor. Inside the relative clause, al que le presté… is the same pattern.

Is that le optional here?

In this structure, it’s strongly preferred and often felt to be required. Many speakers would find al que presté el trapeador odd or wrong. With indirect objects referring to people—especially when they’re fronted or in a relative clause—Spanish almost always doubles with le/les.

Could I use a quien instead of al que?

Yes. El vecino a quien le presté el trapeador… is correct and a bit more formal. You could also say …al cual le presté… (more formal/literary). All three work.

Why al and not a el?

Spanish contracts a + el to al. So a el que becomes al que.

What does me lo mean in me lo devuelve?

me = to me (indirect object)
lo = it (direct object, here the mop)
devuelve = he/she returns So me lo devuelve = he returns it to me. Spanish stacks pronouns before the conjugated verb.

Why is it me lo and not lo me?

Pronoun order rule: indirect object pronouns (me, te, le, nos, les/se) go before direct object pronouns (lo, la, los, las). Hence: me lo, te la, se los, never lo me.

Why not se lo devuelve mañana?

Se replaces le/les when combined with a third-person direct object pronoun (lo/la/los/las) to avoid le lo. But here the indirect object is first person (me), so it stays me: me lo devuelve. Se lo devuelve would mean “he returns it to him/her.”

Does lo agree with trapeador? What if the object were feminine or plural?

Yes, lo matches masculine singular. Change it to match the direct object:

Feminine singular: me la devuelve (e.g., la escoba)
Masculine plural: me los devuelve (e.g., los trapeadores)
Feminine plural: me las devuelve (e.g., las escobas)

What tenses are presté and devuelve, and why present for a future meaning?

presté: preterite, 1st person singular (I lent). It’s a finished past action.
devuelve: present, 3rd person singular. With a future time marker like mañana, Spanish often uses the present to express a scheduled/near-future event. You could also say me lo devolverá mañana or me lo va a devolver mañana.

Can I move mañana to another position?

Yes. Common options:

Mañana me lo devuelve.
Me lo devuelve mañana.
Mañana, el vecino… me lo devuelve. Word order changes emphasis, not meaning.

Is trapeador the standard word everywhere?

It’s common in much of Latin America for “mop.” Regional alternatives exist:

Mexico/Central America: trapeador, also mechudo in some areas
Argentina/Uruguay: lampazo
Caribbean: mapo/mapa in some places
Spain: fregona All are understandable regionally, but trapeador is a safe LatAm choice.

Could I say El vecino que le presté el trapeador…?

No. After a preposition like a, you can’t use bare que. Also, prestar needs the preposition a for the person. So you need al que/a quien: El vecino al que (a quien) le presté el trapeador…

Can I drop me and just say lo devuelve mañana?

You can, but then you’re no longer saying it’s returned to you. Lo devuelve mañana = “he returns it tomorrow” (to someone, unspecified). To keep “to me,” you need me. For emphasis, you can add a mí: A mí me lo devuelve mañana.

If it’s a female neighbor, what changes?

Make the nouns/pronouns feminine:

La vecina a la que le presté el trapeador me lo devuelve mañana. (Only la vecina and a la que change; trapeador remains masculine, so lo stays.)

Can I use regresar instead of devolver?

In much of Latin America, yes: me lo regresa mañana is very common. In Spain, devolver is the standard verb for “return (an item).” Devolver is always correct everywhere.

How do I say “He’s going to return it to me tomorrow”?

Two equally natural options:

Me lo va a devolver mañana.
Va a devolvérmelo mañana. (Both use ir a + infinitive; attaching the pronouns to the infinitive is optional.)

How does the sentence change with plurals?

Plural direct object: El vecino… me los devuelve mañana (e.g., multiple mops).
Plural neighbors (subject): Los vecinos a quienes les presté el trapeador me lo devuelven mañana.
Both plural: Los vecinos a quienes les presté los trapeadores me los devuelven mañana.

Why does presté have an accent but devuelve doesn’t?

Spanish accent rules:

presté is stressed on the last syllable and ends in a vowel, so it needs a written accent to mark the irregular stress.
devuelve follows regular stress on the penultimate syllable; no accent mark needed.

Can the pronouns attach to other verb forms?

Yes:

Infinitive: …va a devolvérmelo mañana (or before: me lo va a devolver)
Gerund: …está devolviéndomelo (or before: me lo está devolviendo)
Affirmative command: Devuélvemelo mañana.
Negative command: No me lo devuelvas mañana.