Kim Kardashian only discovered Tracee Ellis Ross’s 50th birthday party wasn’t a Halloween party when she arrived as part of the X-Men.

The SKIMS founder turned up as Mystique from the superhero franchise - alongside her pals Olivia Pierson, 33, and Natalie Halcro, 34, who dressed as Magik and Selene respectively - without realising the ‘Blackish’ star hadn’t mandated a dress code of fancy dress.

On a selfie of her in her blue body paint and red hair and the birthday girl in a glamorous red outfit the 42-year-old reality television star wrote on Instagram on Sunday (29.10.2022): “That time I showed up to a birthday dinner in full costume when it wasn't a costume party!”

Kim also wished many happy returns to Tracee - who is the daughter of the Motown superstar Diana Ross - labelling her a “beautiful soul”.

She added: “Happy Birthday to the most beautiful soul @traceeelliseross.”

‘The Kardashians’ star also posted a snap of her and and hip-hop mogul Diddy, 52, in his Halloween costume, the Joker.

She wrote: “Never broke character.”

Kim also showed off her nine-year-old daughter North’s costume, a detailed alien garb that the little girl had dreamed up herself.

The 42-year-old star - who also has son Saint six, daughter Chicago, four, and son Psalm, three, with her ex-husband Kanye West - said: “North came up w these prosthetic design.”

Kim had earlier delighted fans when she showed off her costume for the first time, with her donning a skintight blue bodysuit with a scaly finish to portray the shapeshifting assassin.

The former 'Keeping Up With the Kardashians' star completed her transformation into Mystique - who has been played on screen by the likes of Jennifer Lawrence and Rebecca Romijn - with blue face paint, bright yellow contact lenses and a red wig.

In a clip shared to Instagram, she said: “It looks really cool like this."

Kim later shared a video to Twitter, which gave a shout out to Marvel and prompted fans to urge the entertainment company to "make it happen".

Another fan praised the effort Kim had made.

They wrote: “Can’t imagine how hard you had to get into this costume. Reminds me when you starved yourself for Marilyn Monroe dress. Always going all out."