Swift: Natively Detect if App has Crashed

I have searched around, but have yet to find an answer that doesn't direct me towards a 3rd party service. I do not need anything intricate, just to save a value in NSUserDefaults so when the app opens next, I can display an alert saying the app has crashed.

Thanks.

Thanks to a little help from @RyanCollins, I was able to solve the problem myself. The function applicationWillTerminate in the App Delegate only runs when the app closes properly. The code to natively detecting an app crash looks like this.

Globally Defined Variables

let crashedNotificationKey = "com.stackoverflow.crashNotificationKey"
var crashedLastTime = true

App Delegate

func applicationWillTerminate(application: UIApplication) {
    crashedLastTime = false
    prefs.setBool(crashedLastTime, forKey: "crash")
}

func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
    crashedLastTime = prefs.boolForKey("crash")
    if crashedLastTime == true {

        crashedLastTime = false
        prefs.setBool(crashedLastTime, forKey: "crash")
        NSNotificationCenter.defaultCenter().postNotificationName(crashedNotificationKey, object: self)

    } else {

        crashedLastTime = true
        prefs.setBool(crashedLastTime, forKey: "crash")

    }

    return true
}

Root View Controller

override func awakeFromNib() {
    NSNotificationCenter.defaultCenter().addObserver(self, selector: "crashedAlert", name: crashedNotificationKey, object: nil)
}

func crashedAlert() {
    let alert = UIAlertController(title: "The app has crashed!", message: "Sorry about that! I am just a 17 year old highschooler making my first game!", preferredStyle: UIAlertControllerStyle.Alert)
    alert.addAction(UIAlertAction(title: "It's cool bro.", style: UIAlertActionStyle.Default, handler: nil))
    self.presentViewController(alert, animated: true, completion: nil)
}