"The worst has passed already."
Translation:Lo peor ya ha pasado.
"El peor" or "La peor" would be correct if the gender were known. It is not known here, so "Lo peor" is correct. CzarnyCzesio (below) has provided an authoritative link directly in point. http://spanish.about.com/od/adjectives/a/best_worst.htm. My dictionary also confirms the usage of all three forms (lo peor, la peor and el peor) for the noun form of "peor".
Here is the explanation: http://spanish.about.com/od/adjectives/a/best_worst.htm
Puedes ponerlo tranquilamente, sin contexto es imposible saber a que se refiere. Podría referirse a un ciclista, por ejemplo, en una competición en la cual un aficionado le dice a otro "el peor (ciclista) ha pasado ya"...Bien es verdad que yo, como español, lo primero que he pensado ha sido en poner "lo peor ha pasado ya", lo cual no quita que "le" esté igual de bien.
Yeah, we've seen this before with questions about where it's possible to put adjectives, or even where the 'no' goes in making a verb negative. As far as I can tell, you can't split up verbs that go together in Spanish. I think of this as being like the often-challenged rule in English about not splitting infinitives (e.g., 'boldly to go', rather than 'to boldly go'), which we got entirely from Latin (though I'm not sure if it is actually related or not).
''ýa'' is an adverb. As an adverb it must be close before or after a verb, or before or after another adverb, such as the negative adverb "no".
Ya means a lot of things depending on context. In the present tense it means now or already, except in a negative construction when it means no longer. In the past tense it nearly always means ''already'' such as in this sentence. In the future, it means later....Ya lo haré - I'll do it later.
In this sentence I think it works to place Ya either before the noun, before the verb or at the end of the sentence. It generally translates the same given this sentence is in the past tense. It's never placed between the auxiliary verb and the conjugated verb.
From other comments: