The former “Simple Life” star, 41, gave her millions of followers a glimpse into the special bond with her sister Sofia, sharing a photograph of her holding the train of her sibling's custom Chanel wedding dress, as the pair beamed at each other.
Nicole captioned the snap on Instagram: "I love you more than anything."
And in the comments, Sofia, 24, replied: "I love you more than life."
Sofia tied the knot with British music executive Elliot Grainge, 30, at Hotel du Cap-Eden-Roc in Antibes, France, on Saturday, April 22, before family and friends.
The star-studded guest list included Nicole and her Good Charlotte rocker husband Joel Madden, close pal Paris Hilton, and Cameron Diaz and Benji Madden.
Sofia and Nicole's dad, music icon Lionel Richie, walked her down the aisle.
Elliot proposed to Sofia in April last year.
The model subsequently took to social media to announce the news to the world.
Sofia wrote on Instagram at the time: "Forever isn’t long enough @elliot. (sic)"
Sofia, who previously dated socialite Scott Disick - converted to Judaism ahead of her wedding.
As part of her preparations for tying the knot with the businessman, she studied to adopt her partner's faith.
She wrote on her Instagram Story earlier this month: "What a magical day. I want to thank cantor Nathan Lam for helping me along this journey of converting to Judaism. It has been one of the greatest experiences of my life. Today was that day!!!(sic)"
The loved-up pair made their relationship Instagram official last year, when they posted a photo of them kissing.
Meanwhile, Disick tried to "keep busy" in the run-up to his ex's wedding.
The 39-year-old reality star - who has Mason, 13, Penelope, 10, and Reign, eight, with Kourtney Kardashian - dated Sofia between 2017 and 2020, and Disick made a concerted effort to busy himself before the blonde beauty married her beau.
A source told “Entertainment Tonight”: "He is doing his best to focus on the good things in his life, but between Kourtney and Travis Barker' wedding special airing and Sofia’s wedding this weekend, it has been a lot. He's spending time with close friends to stay distracted and keep busy."