Riverdale's Lili Reinhart and Camilla Mendes reunite for Halloween

Riverdale stars Lili Reinhart, Camila Mendes and Madelaine Petsch have reunited for Halloween.

In a joint Instagram post the actresses revealed their group costume, each dressing as a character from DC's Batman. "Gotham city sirens," they captioned the post, referencing the comics series dedicated to the three characters.

Reinhart had opted to dress as Harley Quinn, while Mendes' look was inspired by Julie Newmar's 1966 iteration of Catwoman and Petsch had chosen Poison Ivy.

Related: First look at Riverdale star Cole Sprouse's new Frankenstein movie

This isn't the first time Reinhart, Mendes and Petsch have opted for a group Halloween costume either, with previous costumes including the Hocus Pocus witches and The PowerPuff Girls.

"I love that you guys still did a throuple costume this year!" wrote Riverdale co-star Sarah Desjardins, while a fan added: "Y'all better keep this trio costume tradition forever."

The actresses all starred in the supernatural teen series alongside KJ Apa and Cole Sprouse, which aired for seven seasons, from 2017 until earlier this year.

Following the death of a teenager, a group of school students attempted to unravel the evil mysteries of their town, with later seasons expanding to include cult sacrifices, superpowers and alternate universes.

Related: Riverdale's Madelaine Petsch gets unwanted visitor in first Strangers clip

Earlier this year Reinhart addressed comments made about the show, acknowledging that the Riverdale's storyline's were often made fun of in the latter seasons.

"It's really not been easy to feel that you're the butt of a joke. We all want to be actors; we're passionate about what we do. So when the absurdity of our show became a talking point, it was difficult," she told Vulture. "It is 'What the f**k?'. That's the whole point."

Riverdale aired on The CW in the US and in the UK you can stream via Netflix.

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