It's an oldie, released in 1952. But it's pretty good. Stewart Granger has the lead role, James Mason is the dastardly Count Rupert of Hentzau. Debra Kerr is the Princess Flavia. The costumes are wonderful, both for the men and the women. Granger and Kerr look fabulous entering the royal ballroom. It's in Technicolor. The dialogue is witty and good. There is plenty of daring do, including a sword fight in a castle, a cavalry charge, a gun fight in a deserted urban summerhouse.
Netflix has it, but it's a long wait. I have it on a VHS tape I got from Amazon a long time ago.