Blackstock was married to Clarkson for seven years and they shared two children – daughter River, 11, and son Remington, 9.
They had a tense divorce, engaging in multiple legal disputes over their Montana ranch and music industry contracts.
Blackstock became her manager after they began dating, securing several deals for Clarkson.
In 2023, Blackstock was ordered to pay the singer US$2,641,374 ($4,434,788) for breaching talent agency laws in respect of his management.
He had previously been receiving monthly spousal support of US$45,000 from his ex-wife.
Clarkson cancelled the remaining shows in her Caesars Palace residency shortly before Blackstock’s death.
In the announcement, she referenced his illness and said she needed to be “fully present” for their children.
She was not named in Blackstock’s obituary and is yet to comment on his death.