Los Angeles, California - Khloé Kardashian penned an emotional message to honor Tristan Thompson's younger brother, Amari, on his 18th birthday.

KoKo took to Instagram on Saturday to share a slideshow of photos with Amari along with a sweet caption.

"I can't believe you are 18! You have changed our lives in the best possible ways!" she wrote. "Thank you for being an angel to us all! You are the sweetest, silliest and most loving young man.

"I hope you feel how much we love and adore you our sweet angel Amari."

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Throughout the carousel post, Amari was seen posing with Khloé and her two kiddos, True and Tatum, as well as the extended second-generation Kar-Jenner crew.

Following the sudden death of Amari and Tristan's mom last year, the 40-year-old reality star opened her home to both her ex and his younger brother.

Amari, who suffers from epilepsy and other medical conditions, has been under Tristan's legal guardianship since their mom's passing.

Despite the NBA star's repeated infidelity during their relationship, Khloé and Tristan have managed to stay on very good terms as they co-parent True and Tatum.

Earlier this year, the Good American mogul celebrated Tristan's birthday with another heartfelt tribute in which she told him, "Your mommy is proud of you."