What to tell children during Parental Separation?

My wife of 18 years and I have decided to split, albeit amicably. I am going to get my own place, close by to be near the kids, age 11 and 14. My question is what is the best way to let the kids know about this move. I want to tell them gracefully, and sure they have an idea this is inevitable. Thanks for the help in advance during these tough times.