Supervene

[Sarah]

To come as something additional or extraneous; to occur withreference or relation to something else; to happen upon or aftersomething else; to be added; to take place; to happen.Such a mutual gravitation can never supervene to matter unlessimpressed by divine power. Bentley.A tyrany immediately supervened. Burke.

[Agnes]

to happen in the middle of a situation that already exists, and change that situation:

[GarryDrold]

Occur later than a specified or implied event or action, typically in such a way as to change the situation.