Can I use "at the end" the same way as "at last"?

Question

He has been waiting for this letter for days, and at last it has come.

Can I use "at the end" instead?

Answer 1

The correct idiomatic expression is:

In the end:

• Eventually; ultimately: All will turn out well in the end.

(AHD)

Compare:

In the end:

• In the end is used mostly as an idiom that means "finally," "after a long time," or, "when everything is considered.*" It is often followed by a comma.

Here are some sentences with this idiom:

• We worked hard, and in the end, we achieved our goal. In the end, what really matters in a friendship is trust.

At the end:

• At the end is used in the idiom "at the end of the day." which means something similar to in the end (= when everything is considered)
• However, at the end is most commonly used more literally, as a prepositional phrase followed by of, to refer to the end of a specific noun. This noun can be a physical object, a period of time, an event, a place, or something more abstract, such as one's patience.

Here are some sentences with at the end + of:

• At the end of his life, he had no regrets. Put a period at the end of every sentence. I pay the phone bill at the end of each month. There is a brick building at the end of the driveway.

(M-W)

Answer 2

The expression in the end could be used, but I feel that the adverb, finally, sounds more natural to my ears.

He has been waiting for this letter for days, and finally it's come.

Contracting "it has" to "it's" improves the flow still.

finally
after a long time, typically when there has been difficulty or delay. "he finally arrived to join us"

synonyms: eventually, ultimately, in the end, by and by, at length, after a long time, after some time; at long last, in the long run, when all was said and done, in the fullness of time; informal: at the end of the day

Oxford Dictionaries