According to sources, Viall texted Stanton after proposing to another woman at the end of filming his The Bachelor edition, Life & Stylereported.
"He texted Amanda once news broke of her breakup," an insider revealed, claiming Viall was secretive about the message exchange. "He wanted to reach out and say, 'Hey,' but that's not what a happily engaged guy should be doing!"
News of Stanton and Murray's split began circulating in December, yet the mother of two didn't confirm they had called it quits on their short-lived engagement until earlier this month.
"Josh and I did break up," Stanton, 26, told People at The Bachelor Charity Premiere Party in Los Angeles on January 2, adding that they're not on speaking terms and there are just "some things you can't fix" about the person you love.
"There was a lot of different reasons. At the end of the day, we were just two very different people."
Stanton and Murray, 32, got engaged on the third-season finale of Bachelor in Paradise, which aired in September. The couple became invested in one another on the show only after Murray stole Stanton away from Viall, who took Stanton on a date and kissed her first.
Viall and Murray had an ongoing rivalry on Bachelor in Paradise over the pursuit of Stanton and their history of fighting for the same girl, Andi Dorfman, on Season 10 of The Bachelorette. (Murray had won Dorfman over and the pair was briefly engaged).
Once Murray and Stanton's physical chemistry became clear to everyone in Paradise, Viall gave up on his romance with the beautiful blonde and moved on with new arrivals.
After Stanton confirmed to the press her relationship with Murray had failed, the former pro baseball player made a statement of his own.
"Our relationship, it just wasn't working out and it sucks," Murray told Us Weekly on January 3. "I moved across the country for her, I fell in love with her kids, really loved her family, but we just weren't able to grow together as a couple and it was very frustrating."
Murray added, "We have similar things we want in life, but we are also very different on other important things as well."
Stanton had been warned by her Bachelor in Paradise castmates -- including Viall -- that Dorfman accused Murray in her memoir of being verbally abusive, temperamental and controlling during their romance a couple of years back. Murray, a former Famously Single participant, called it all "fiction" at the time.
Murray moved to Stanton's home in Orange County, CA, shortly after Paradise concluded and appeared to become a loving stepdad to her two young daughters from her previous marriage to Nick Buonfiglio -- Kinsley, 4, and Charlie, 2.
However, Murray headed back to his home base of Atlanta, GA, following the split, which was reportedly made official after the pair got into a heated argument at KIIS FM's Jingle Ball concert last month over Stanton allegedly drinking alcohol on a vacation with her girlfriends.