I'm a new team lead on a project integrating my companies' software with an outside vendor's. This project was planned out and estimated before I came on, so I'm pretty much just following the roadmap.
However, we just got a delivery from the vendor requiring a completely new method of communication between our code and theirs. This was completely unplanned-for work that must be done immediately and will require a decent amount of effort, which will push out our other planned features. I've also found out that this vendor has been known for springing these "surprises" in the past.
Basically, I need to tell my boss that we just got told about feature X, which will require Y hours of work to do, which will push out features A, B, C, without sounding too much like a complainer. What's the best way to do that?