Your question is Communicate Sponsor Bad News. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
You are leading a project that is off track against a committed delivery plan. A material issue has emerged that will affect either timeline, scope, or risk, and you need to update the project sponsor before they hear it elsewhere.
Describe a situation where you had to deliver bad news to a project sponsor. How did you handle it?