I am using the Advanced Custom Fields plugin on WordPress - with no other plugins. When a user creates a new post, I am using the relationship field from ACF so the user can select related posts (custom post type). I want the user to be able to click a button 'create new related post' which creates a popup (still on the create new post page). The popup allows the user to create a related post with a custom post type. Once they publish it, the popup disappears and the ACF relationship field is refreshed to show the new post, allowing the user to select it. Make sense?