The 'Skyscraper' singer joined Kardashian and other friends to celebrate the reality star's impending nuptials to basketballer Kris Humphries.
Lovato wrote on Twitter after the event: "Had such a fun time at @KimKardashian's bridal shower. God that family is gorgeous! (sic)"
Kardashian then replied: "I love u & remember what I told u! ;-)", prompting Lovato to respond: "I love you. And I won't forget... You totally are my big sister... Hahaha."
Kardashian concluded the conversation by writing: "Always little sis!"
Lovato previously branded the Keeping Up With The Kardashians star her "style icon", with Kardashian later saying she was "flattered" by the praise.
Other celebrity guests at the wedding shower thrown by Kardashian's mum Kris Jenner included Kelly Osbourne, Mel B and Serena Williams, as well as Kardashian's siblings Khloe and Kourtney.
Kardashian, who became engaged to New Jersey Nets star Humphries in May, also celebrated her bachelorette party over the weekend, throwing a bash at Tao nightclub in Las Vegas that was attended by her mum, sisters and close friends.
She also made a brief appearance at fiancé Humphries's own bachelor party which was taking place at the nearby Lavo nightclub.
> Kim Kardashian will be embarrassed at bachelorette party, says Kourtney Kardashian
> Demi Lovato: 'I'm on cloud 19 with 'Skyscraper' success'
Watch a promo for Keeping Up With The Kardashians' current season below: