You are in the middle of a sprint and suddenly the product owner comes with a new requirement, what will you do?

In an ideal case, the requirement becomes a story and moves to the backlog. Then based on the priority, the team can take it up in the next sprint. But if the priority of the requirement is really high, then the team will have to accommodate it in the sprint but it has to be very well communicated to the stakeholders that incorporating a story in the middle of the sprint may result in spilling over a few stories to the next sprint.