Last Christmas Wham!
Up and coming US actress will play Lady Di
Chastain, who's recently starred in The Tree Of Life, The Help and The Debt, will play the Princess in "Caught In Flight".
The biopic will tackle the secret love affair between Diana and heart surgeon Dr Hasnat Khan and is will be directed by Oliver Hirschbiegel, who's also worked on Borgia and Downfall.
The film is said to be going in pre-production next March, according to Thompson on Hollywood.