The acting royalty have each announced that they are 'amicably' splitting from their long-term partners within six months of each other.
Casey, who is the younger sibling at 40 years old, has been married to wife Summer Phoenix since June 2006 and they have two children together, Indiana, 11, and Atticus, eight.
Casey and Summer
Ben, 43, has been married to actress Jennifer Garner since 2005 and they have three children, Violet, Samuel and Seraphina Rose Elizabeth.
The Gone Girl actor appeared on the Ellen Degeneres show in the USA to explain how he and Jen are managing to live on the same estate in California and trying 'co-parenting'.
Ben and Jennifer
Ben said; 'We are good friends and we're doing our best and the kids are fabulous and we're working on our best for them.'
Speaking to Vanity Fair magazine the Argo director added; 'Jen's great... she's a great person. We're on great terms, I just saw her this morning so that's the reality that I live in.'
Jennifer said; 'It's not easy to go through it, period. I have found going through it in the public eye, it's just another facet of it. For anyone, when your life shifts in any way, it's tricky enough.'
Ben and Casey
Brother-in-law Casey has also stressed that the divorce proceedings between him and his wife, who is the youngest sibling of Joaquin and River Phoenix, will follow in his brother's amicable footsteps.
A spokesperson said; 'Casey and Summer have amicably separated. They remain very close friends.'
Ben and Casey in Good Will Hunting with Matt Damon
Interstellar actor Casey was introduced to Summer by her brother, Joaquin, in 2000 and they dated for six years before finally walking down the aisle in Savannah, Georgia.
Casey currently lives in Los Angeles and 2016 will see him take to the screen in three new film productions, Disney's The Finest Hours, Triple 9 with Kate Winslet and Manchester by the Sea with Michelle Williams.