Another option is actually not technically English but nonetheless used by English speakers. You can say "and voilà!" Yes, we English speakers use a lot of foreign vocabulary, especially from French. It adds a certain... "je ne sais quoi" ;)

If you want to add some humor you could say Bob’s your uncle. You could also say By the grace of God. Or you could say And wouldn’t you know it.

That saying is very archaic. "All of a sudden", " To my amazement" or, " Out of nowhere.", etc, is the closest I can think of.

Thank you Hasmik, the context is a bit long to explain here, but I will consider your options

I think “aha”, “there!” “oops” or maybe “suddenly “ can be alternatives depending on the context :)