Inevitably means in a way nobody could possibly prevent. It was always going to end like this.
The word does two jobs. Genuinely, it marks something as unavoidable, as in the costs inevitably rose. In storytelling it is often a wry aside, since inevitably, it started to rain admits that this is exactly what you would expect. That second use is very common in British speech. The adjective inevitable is the one you meet in the phrase the inevitable happened, and the noun inevitability is used mainly in serious writing.
1adverbinevitablyIn a way that cannot be prevented or avoided.
“Delays inevitably followed the change of plan.”
Also accepted in games: unavoidably
Latin
inēvītābilis — unavoidable
Middle French
inevitable
English
inevitable
English, today
inevitably
Built from
From inevitable + -ly. inevitable comes from Middle French inevitable, from Latin inēvītābilis (“unavoidable”), from in- + ēvītābilis (“avoidable”), from evito (“to avoid”), from ē- (“out”) + vito (“to shun”).
Etymology from Wiktionary, CC BY-SA