With filming under way on the sixth Harry Potter film, Newsround can exclusively reveal that actress Helen McCrory will play Narcissa Malfoy.
The Potter team have been after her for a while.
She was originally cast as Bellatrix Lestrange in the fifth Potter movie, but couldn't play the part because she was expecting a baby.
Now she's set to play Draco's mother and Bellatrix Lestrange's sister, who's played by Helena Bonham Carter.
Now the two will end up playing sisters in Harry Potter and the Half-Blood Prince.
Other casting includes Jim Broadbent as Professor Horace Slughorn.
An announcement on who will play young Tom Riddle and Lavender Brown is expected very soon.
Harry Potter and Half-Blood Prince is due to hit cinemas towards the end of 2008.