Learn French: L'horoscope annonce de mauvaises nouvelles.

When a plural adjective comes directly before a plural noun, the plural indefinite article des changes to de. Since the adjective mauvaises comes before the noun nouvelles, we use de instead of des.

Why does mauvaises come before the noun instead of after it?

Most French adjectives come after the noun, but a short list of common adjectives goes before it. You can remember these with the acronym BANGS, which stands for Beauty, Age, Number, Goodness, and Size. Mauvais means bad, which falls under Goodness, so it goes before the noun.

Why is nouvelles plural in French when 'news' is singular in English?

In English, 'news' is an uncountable noun (we say 'the news is bad'). In French, une nouvelle is a countable noun meaning 'a piece of news'. Because the horoscope is giving multiple pieces of news, French uses the plural nouvelles.