What's the difference between "sadly" and "unfortunately"? Are they always interchangeable?

Rebecca

"Sadly" and "unfortunately" have very similar meanings and are often used interchangeably, however, there is a slight difference in the nuances between them. "Sadly" refers to something which is sad to have happened or has caused grief or sorrow. "Unfortunately" can mean the same thing, however, it more specifically refers to something which has happened by chance or misfortune. Ex: Unfortunately, I didn't win the lottery. Ex: Sadly, my cat died.