Learn Spanish (Latin America): Lo siento, señor García.

Exactly! Literally, lo siento translates to "I feel it," but it is the standard Spanish phrase for "I'm sorry." You use it as a set phrase to express regret or sympathy.

I learned that we use el with titles. Why isn't it el señor García here?

You use el (or la) when you are talking about someone, like in the sentence el señor García es profesor (Mr. García is a teacher). But when you are speaking directly to the person, like we are doing here, you leave the el out.

Why is señor written with a lowercase "s"?

In Spanish, titles like señor, señora, and doctor are not capitalized when you write out the full word. You only capitalize them if you use their abbreviations, like Sr. or Sra.

If I wanted to ask Mr. García how he is doing right after this, would I use the informal tú or the formal usted?

You would use the formal usted. Whenever you address someone by a title and their last name, like señor García, it means you are in a formal situation or showing respect. Therefore, you must match that respect by using usted instead of the casual tú.