HARRY POTTER star Rupert Grint has revealed how both he and co-star Daniel Radcliffe are growing up - their voices have broken.

He admitted: "My voice is a lot lower than it was in the last film."

Rupert, 13, who plays Ron Weasley in the film series, says that his own voice started changing at the start of shooting the latest movie, Harry Potter And The Chamber Of Secrets.

He said: "It's strange. Dan's has broken completely. But they had decided that they were going to break it in the film anyway, so it hasn't been a problem with the producers."

Rupert will be joining all the other main cast members, including Daniel and Robbie Coltrane, tomorrow for the launch of The Philosopher's Stone on video and DVD.

The cast will appear on the Hogwarts train at Kings Cross Station, platform one, for the launch of the video and DVD on Saturday.

Rupert is back on screens this month in new kids' movie Thunderpants, in which he plays a young boffin Alan A. Allen. The movie features cameos from Leslie Phillips and Stephen Fry.

The young actor is becoming a big star, and is even receiving his own fan mail. He said: "I get lots of letters from girls and it feels really weird, but it's funny as well."