'Alaskan Bush People' Star Rain Brown Mourns Death of Her Father Billy Brown: 'My Hero'

Billy Brown's family is mourning the death of their patriarch.

The Alaskan Bush People star died on Sunday night after suffering a seizure. He was 68.

Following the news, Billy's daughter Rain, 18, called her father "the closet thing to an angel I've ever known," in a touching Instagram tribute.

"I lost a true friend. Not forever, but only in this world. Please hold my family in your thoughts and prayers, especially my mother," she wrote. "Please hold your family tight for me. Words cannot express how wonderful he was and is. But I will say, the closest thing to an angel I've ever known. God bless you da [sic] I love and miss you dearly. You will always be my hero. God bless everyone."

Along with the message, Rain, the youngest of Billy's seven children, shared a photo of herself with her dad and mom, Ami Brown.

One of Rain's five brothers, Noah, 28, shared a photo of his father holding his young son Elijah Connor Brown, whom he shares with wife Rhain, in his own Instagram tribute.

Billy was also father to sons Matt, Bam Bam, Gabe, Noah and Bear, as well as daughter Snowbird.

Bear, 33, announced Billy's unexpected death on Monday.

"We are heartbroken to announce that our beloved patriarch Billy Brown passed away last night after suffering from a seizure," he wrote on his Instagram account. "He was our best friend — a wonderful and loving dad, granddad and husband and he will be dearly missed."

"He lived his life on his terms, off the grid and off the land and taught us to live like that as well," he continued. "We plan to honor his legacy going forward, and to continue with his dream. We ask for privacy and prayers during this painful time. God Bless Everyone!"

Billy had starred in the Discovery reality series alongside his family since 2014.

"We are devastated to hear of Billy Brown's sudden passing," a spokesperson for Discovery said in a statement to PEOPLE. "He has been part of the Discovery family for years — a trailblazer, a lovely man and most definitely one of a kind. Our heart is with his family and those that knew him and loved him as they deal with this devastating loss."