Execution of a watcher when another one has been executed

There is a watcher history index that contains information about all watch executions. You could query that one as part of your watch.

GET .watcher-history-*/_search
{
  "size": 1,
  "query": {
    "bool": {
      "filter": [
        {
          "term": {
            "watch_id": "my_watch"
          }
        }
      ]
    }
  },
  "sort": [
    {
      "trigger_event.triggered_time": {
        "order": "desc"
      }
    }
  ]
}

Hope this helps!

--Alex