From the perspective of Catholicism are there any non-Catholic saints?

I'm writing about Catholicism and from what I extracted of a conversation with a priest friend of mine, > When we ask a Saint for intercession, we need to know that person is alive in heaven. Before that person becomes a Saint, there's a process that requires something extraordinary to happen; when the person isn’t yet considered a Saint, we can have private devotion to them, ***as long as they were Catholics***, and ask for intercession; if something extraordinary happens it can serve to beatify / sanctify that person. This got me wondering... are there any non-Catholic saints?