They may or may not know about it right away, but if you do not tell the court up front, you risk the judge finding out later and demanding an answer. The judge may also order another hearing to determine if the sentencing was made on information that was not complete. You definitely want to avoid that. Hope this helps!
The court will know about it. It could mean that any plea deal you have goes out the window, allowing the judge to sentence you to whatever he or she wishes within the law. Obviously, you'll have this new charge to contend with as well.
