A ninth 'Harry Potter' movie is being secretly filmed.

A ''mini movie'' is currently being shot at the Potter studios in Hertfordshire, south east England, and will be screened at some of the franchise's theme parks.

Helena Bonham Carter has been spotted reprising her role as witch Bellatrix Lestrange for the follow up film to 2011's 'Harry Potter And The Deathly Hallows - Part 2', which was billed as the final motion picture based on J.K. Rowling's popular book series, which spawned eight big-screen productions.

A source told The Sun newspaper: ''The cast have really enjoyed getting back together -- they are so tight-knit.''

The mini film will be screened at The Wizarding World of Harry Potter attraction in Florida and two new Hogwarts theme parks, one in California and another in Japan, which are currently under construction and are due to open in 2014 and 2016 respectively.

Insiders revealed filming for the short film - plot details of which have not been revealed - has been ''intense''.

The source added: ''The shooting schedule is nowhere near as long as the films, so though filming has been intense, the stars have enjoyed being able to pop in and out.''