A source close to Brinson tells ET that his family, including Richards, is gathering around him as he's been moved to an assisted living facility, and "nobody knows at this point how much longer he’ll last."
"He seems to mentally be good most of the time, he is just on a lot of medication," ET's source shared.
Richards has been "by his side quite often," the source said, adding that the 51-year-old reality star has "been holding up well" and that she's "at peace with Monty's diagnosis."
Brinson appears to be at peace with his terminal illness as well. He has been open about his battle with cancer in numerous posts shared to Instagram over recent weeks, opening up about his struggle with his friends and followers.
"I'm surrounded by love," Brinson wrote in a caption to a post shared on Monday. "I got plenty of love in my heart. I'm here for everybody. This might be my final resting place but I'm content."
In an Instagram post that has since been deleted, Brinson opened up about how difficult it is for him to type, sharing, "I have a friend that will be [here] to help [me] for a few weeks." Much of Brinson's deleted message, originally posted on Monday, was almost indecipherable, and served as a stark look at the challenges his struggle with cancer has presented him.
Back in December, Brinson shared a story about being visited by a minister who wanted to talk to him about life and death.
"I'm not a quitter and no matter what you go through don't be a quitter. No matter your situation," Brinson wrote. "A minster Walked into my room out of nowhere. Asked me if I would like to talk about Life and Death, I said no, cause I'm not scared of death I choose life lll just dig down inside and get all my energy and fight back."
In an earlier post, in which Brinson shared a stunning photo of a colorful waterfall, he wrote, "My entire life has been like [a] ticket at Disneyland. I've lived thru the highest highs and the lowest lows. Isn't that Life? #thankful #family #blessed #love #life."
"Everyone has had a lot of time to be with Monty during all of this and had their time to process his illness," ET's source shared regarding Brinson's failing health. "Everyone is visiting Monty all the time, his family is always gathering around him."
Richards and Brinson tied the knot in 1985 before welcoming their daughter, Brooke, in 1986. The couple eventually divorced in 1988, but maintained an amicable relationship.
Brinson showed his love and support for Richards on Instagram, sharing a photo of the couple in their younger years and captioning the throwback pic with a supportive message for his embattled ex
that read, "I'm excited for her. And personally I would like to thank everyone who stood by her through this rough time."