How do you figure out which Hollywood star donned the most costly bling in a movie?

The home-insurance experts at Confused.com decided to create a seed list of famous jewellery worn on the big and small screens. They relied on fashion magazines like Vogue and Harper's Bazaar and jewellery publications like The Adventurine.

Then they put these pieces into different categories, highlighting the carat size, shape, setting, and material.

Then, they asked the jeweller Queensmith to offer valuations.

Queensmith concluded that The Heart of the Ocean necklace, worn by Kate Winslet's character in Titanic, Rose DeWitt Bukater, was the most valuable piece in Hollywood history.

Its value was pegged at $640,459,047.

The Heart of the Ocean necklace featured a 56-carat heart-shaped blue diamond, which was inspired by the Hope Diamond.

The runner-up was "The Toussant" Cartier necklace worn by Anne Hathaway's character, Daphne Kluger, in Ocean's 8. It clocked in at $192,177,700.

That piece had different sized diamonds, including a 136.25-carat blue-white Queen of Holland gem.

The third-place finisher was from a more recent film, Death on the Nile, directed by Kenneth Branagh. Gal Gadot's character, Linnet Doyle, sported a 128-carat Yellow Diamond necklace valued at $38,435,540.

It was a recreation of the famous yellow Tiffany diamond, which as discovered in South Africa in 1877.

TV's most expensive jewellery was a tie between Blair Waldorf's engagement ring in Gossip Girl and Princess Diana's engagement ring in The Crown. Each was deemed to be worth $640,975.

“Jewellery is often covered under your home insurance policy up to a specific value," Confused.com insurance expert Jessica Willock said in a news release. "If your items exceed this value, they would need to be declared separately. Make sure you check with your insurer to see if you’re covered when taking out your policy, to keep high-value items suitably protected.”