Well, without having read the novel, it's all speculation. However, if we break down the title, 'the latest' gives a sense of it being something new or recent. 'Bombshell' often implies something that has a big impact, like a bombshell announcement. So in the context of a novel, it could be a new piece of information that completely changes the direction of the story, perhaps a character's true identity being revealed, or a long - held secret that when exposed, causes chaos among the other characters and the overall plot.
Since I don't have more information about this novel, it's hard to say exactly. But generally, a title like 'the latest bombshell' might suggest that there is some sort of unexpected and perhaps scandalous or extremely impactful element in the story. It could be a new discovery, a character's secret being exposed, or a sudden turn of events that shakes up the whole narrative.