According to the Project Management Body of Knowledge (PMBOK) Guide, when a new stakeholder joins the project, especially one who can significantly influence the project's direction, the project manager should first ensure that this stakeholder has a clear understanding of the project. This includes the project's objectives, scope, deliverables, milestones, and risks. By presenting the project to the new stakeholder, the project manager can align the stakeholder's expectations and decisions with the project's goals and constraints. This is crucial to maintain the project's progress and manage the change effectively. References: Project Management Professional (PMP) Reference Materials, PMBOK Guide, Chapter 13: Stakeholder Management.