Nobody likes a know-it-all, but we weren't wrong when predicting Christopher Nolan's Dunkirk would be a blockbuster. The WWII movie held the number one spot at the box office its first weekend out, having released on July 21.

If you've seen the film already, which revolves around over 300,000 Allied soldiers being evacuated during WWII, perhaps you noticed the under-the-radar cameo by none other than Michael Caine.

It's only now come to light that the actor, who's been in all of Nolan's movies since 2005 (Batman Begins, The Prestige, The Dark Knight, Inception, The Dark Knight Rises, Interstellar) makes a surprise appearance in the wartime film.

Well, sort of.

If you're scratching your head and thinking, "Hmm, I didn't see Michael Caine, and I would totally remember." That totally makes sense, but you may, however, have heard him.

Caine lends his voice to the film early on when he's heard talking to an RAF pilot over the radio.

So how did this come to light? When chatting with NJ.com, Nolan was asked, "Stop me if this is meant to be a secret, but is that a Michael Caine cameo we hear early in the film?"

Apparently, it's not meant to be a secret, and if it was, it's now out, with Nolan congratulating the journalist, saying, "Yes, good for you for spotting him. It's shocking to me that a lot of people haven't, when he has really one of the most distinctive voices in cinema."

He went on to say, "I wanted very much to squeeze him in here. It's a bit of a nod to his character in Battle of Britain."

If you need a refresher, here's a look at Caine in the 1969 WWII film Nolan's referring to, also starring Laurence Olivier and Trevor Howard:

https://www.youtube.com/watch?v=pG3vjhVsE78

Nolan sums up his decision to cast Caine in the flick, simply saying, "And also, it’s Michael. He has to be in all my films, after all."

Dunkirk — starring newcomer Fionn Whitehead, Mark Rylance, James D'Arcy, Harry Styles, Cillian Murphy, and Tom Hardy — is currently in theaters.

If you missed it the first time around, we caught up with Nolan and the cast on the red carpet of the NYC premiere:

[bbca_video_embed media_id="1005580867945" video_id="tqKlH5Gffsaz"]

Did you detect that was Michael Caine on the other side of the radio?