According to the PMBOK® Guide, specifically within the Identify Stakeholders and Identify Risks processes, project management is an iterative effort. New information must be integrated into the project ' s formal records as soon as it is discovered.

Identifying the Stakeholder: Stakeholders can be identified at any point during the project life cycle. When a " new " stakeholder appears in a meeting and begins to influence or provide input on the project, the project manager must first document their presence in the Stakeholder Register. This document captures their interests, involvement, interdependencies, and potential impact on project success.

Identifying the Risk: One of the primary responsibilities of any stakeholder is to assist in identifying risks. According to the Identify Risks process, the project manager should never ignore a potential threat or opportunity. The first step after a risk is identified is to record it in the Risk Register. This ensures the risk is tracked and can subsequently undergo Qualitative and Quantitative Risk Analysis to determine the appropriate response.

The " Identify First, Act Later " Rule: In PMI methodology, you must always document and analyze a situation before taking corrective action (like testing or mitigation). By updating both registers, the project manager ensures that the project ' s scope of influence and its risk profile are accurate and up-to-date.

Analysis of other options:

Option A: Ignoring a stakeholder is a violation of project management principles. Any person who can affect or be affected by the project must be managed, regardless of when they join.

Option B: Performing testing is a Risk Response (Mitigation). You cannot implement a response until the risk has been formally identified, recorded in the register, and analyzed for its probability and impact.

Option C: The Lessons Learned Register is for documenting knowledge gained during the project to improve future performance. While this situation might eventually be a lesson learned, the immediate next step is to manage the active risk and stakeholder during the current execution phase.

Per PMI standards, the project manager must maintain transparency and control by ensuring all Project Documents reflect the current reality of the project environment. Documenting the new stakeholder and the new risk is the essential first step in the Monitor and Control cycle.