add_to_court_and_entourage_effect

add_to_court_and_entourage_effect = {
	save_scope_as = companion
	if = {
		limit = {
			scope:companion = {
				NOT = {
					is_courtier_of = root
				}
			}
		}
		root = {
			add_courtier = scope:companion
		}
	}
	if = {
		limit = { 
			root.current_travel_plan ?= {
				NOT = {
					any_entourage_character = { this = scope:companion }
				}
			}
		}
		root.current_travel_plan = { add_companion = scope:companion }
	}
	if = {
		limit = { 
			scope:activity ?= {
				NOT = {
					any_attending_character = { this = scope:companion }
				}
				scope:companion = { can_join_activity = scope:activity }
			}
		}
		scope:companion = {
			add_to_activity = scope:activity
		}
	}
}

As written in game/common/scripted_effects/00_activity_effects.txt.