The project charter was just approved and the project sponsor has given permission to proceed...

The best option for the project manager in this situation is to have a meeting with the project manager of the other project to find a resource optimization solution that works for both projects. Resource optimization is a technique that aims to balance the demand and supply of resources across multiple projects and ensure that the resources are used efficiently and effectively. By meeting with the other project manager, the project manager can discuss the resource availability, requirements, constraints, and priorities of both projects and explore possible alternatives to resolve the resource conflict. Some of the alternatives may include:

Sharing the resource between the projects according to a predefined schedule or allocation percentage

Adjusting the project schedules or activities to reduce the resource overlap or dependency

Finding another resource with similar skills or qualifications to replace or supplement the requested resource

Negotiating with the stakeholders to modify the project scope, quality, or budget to accommodate the resource limitation

By collaborating with the other project manager, the project manager can find a mutually beneficial solution that minimizes the impact on both projects and maintains a good working relationship with the other project team123. References: = PMBOK® Guide, Sixth Edition, pages 318-319, 333-334; Agile Practice Guide, pages 28-29, 50-51; How to Manage Resources Across Multiple Projects.