What is another word for just knew?
Pronunciation: [d͡ʒˈʌst njˈuː] (IPA) 
There are various synonyms for the phrase "just knew," which means a sudden understanding or knowledge about something. Some of the synonyms for "just knew" include "had a gut feeling," "intuitively sensed," "had an inkling," "felt a hunch," "had a premonition," "had a notion," "perceived instantly," "had an epiphany," "recognized immediately," "had insight," "discovered suddenly," and "realized without explanation." All these synonyms indicate the same sudden and deep understanding about something, which comes without any logical or rational thinking. Thus, these synonyms can be used interchangeably to express the feeling of suddenness and clarity about any situation.
