Can anyone tell me what kind of notice of a qualfiying event needs to be provided by the Employee to the Employer during a divorce?

[Guest Degrandville]

I understand the employee is responsible to give the employer notice after the qualifying event. But, how much and what kind of notice is necessary? If the employer knows that a divorce occurred and starting providing benefits to the ex-spouse, is that enough notice? Or does the employee or his attorney have to write the employer and specifying tell them that a qualifying event occurred? Or is a telephone conversation enough? Does it matter if the conversation happened before or after the divorce?