Garoppolo explained during an appearance on Freakonomics Radio's The Hidden Side of Sports he became friends with both Brady—with whom he shares an agent, Don Yee—and Jacoby Brissett during their time together in the Patriots' QB room:
"We always had a good relationship. Initially when I was younger, kind of like an older brother type of relationship, but as I got older and matured through the NFL, we became closer and we became good friends. You know, we still text here and there. Jacoby was a good friend of mine, too.
"So, the three of us always were texting each other. Everyone said it was a terrible decision to have the same agent, but I think it worked out very well. Our agents look out for both of us, both of our best interest. But at the end of the day it's the NFL. It's a business."
New England selected Garoppolo in the second round of the 2014 NFL draft as the potential heir apparent to the team's quarterback throne.
Instead, Brady has continued to excel in his 40s, which led the organization to trade the promising backup after just 94 regular-season pass attempts in three-plus seasons.
Garoppolo previously told Bleacher Report's Joon Lee the pair enjoyed a strong, competitive relationship during their time together. He remembered one-on-one battles with the three-time NFL MVP that focused on throwing footballs into a trash can.
"There would be days where one of us would win and you wouldn't talk to the other for a little while," he said. "We'd be fine the next day, but it was one of the best things for me. We would push each other, and we got two Super Bowls out of it."
Garoppolo enjoyed immediate success with the 49ers following the deal last season as the team won each of his first five starts after it began the year 1-10.
He's going through some growing pains early in his first full season as a starter, though. He's completed 55.9 percent of his throws for 467 yards with three touchdowns and three interceptions through two weeks.
Perhaps Jimmy G will reach out to his former mentor before Sunday when he'll look to get back on track as the Niners face off with the Kansas City Chiefs.