Warner Bros. Pictures said casting on the sixth installment in the franchise about a boy wizard and his magical friends and foes is now complete.
Broadbent has previously starred in "Iris" and "Moulin Rouge" while McCrory has acted in "Becoming Jane" and "The Queen."
They will play Potions Professor Horace Slughorn and Narcissa Malfoy respectively.
David Yates, who directed the blockbuster, "Harry Potter and the Order of the Phoenix," will also helm "Harry Potter and the Half-Blood Prince."
"I am really excited that David Yates and all our cast are back for the sixth film and welcome some wonderful new additions to our ensemble. We all share a commitment to Jo Rowling and to Harry Potter fans around the world to keep making these films the best they can be and, as we head into the final installments, I can promise that this level of commitment will not waver," producer David Heyman said in a statement.
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