The new film is set over a weekend in the early 1990s when Diana spent the festive season with the rest of the Royal Family at Sandringham, at the peak of her marital issues with Prince Charles.
Ahead of the film’s debut at the Venice Film Festival, Jonny said he was impressed that Spencer is “darker and stranger than most films about the royals seem to be”.
“It’s not The Crown,” he told PA. “There are lots of claustrophobic handheld camera action following her around and you feel straight away that this is not as easy a viewing experience as something like The Crown. It is just doing something different.”
Jonny noted that when composing the score, he initially wanted to include music that Diana was personally a fan of, before taking a different approach when he hit a “dead end” with his initial idea.
“[The music] just needed to describe that situation and describe the oppression she feels in [the] three days she is in this palace in Sandringham”, he explained.
“It’s a bit like a horror film in a way. There are all these sinister servants loitering under stairs and there is this feeling of paranoia and oppression. The music was meant to enhance that.”
Princess Diana was recently portrayed in The Crown by Emma Corrin, who won a Golden Globe and has been nominated for an Emmy for their performance.
Elizabeth Debicki will take over the role when The Crown returns for its fifth season in 2022.
Naomi Watts has also played Princess Di on the big screen, appearing in the ill-fated 2013 biopic Diana.
Spencer is scheduled to arrive in UK cinemas on 5 November.