Garoppolo left the Patriots in October having failed to usurp Brady as the starting QB in New England.
The 26-year-old joined San Francisco 49ers and finished the 2017 season with 1,560 passing yards, seven passing touchdowns, five interceptions, 11 rushing yards, and one rushing touchdown.
Garoppolo had been seen as Brady’s successor though the five-time Super Bowl winner is still going strong at the Patriots.
Brady will be 41 before the new season starts but is expected to again play a starring role.
Garoppolo and Brady regularly trained together and the 49ers man has now revealed details of the pair’s relationship.
“The competitiveness between the two of us was very similar,” Garoppolo told Bleacher Report.
“If I’m playing my best friend in one-on-one basketball, if we are both into it, by the end, we are going to hate each other.
“That’s how it is. All the good competitors have that.
“We got along, but there were always times where we wanted to kill each other. It was a healthy, competitive relationship.
“When I first got [to New England], I thought in my head, ‘I’m better than this dude.’
“It was always a quiet confidence. I would never speak that.”
Garoppolo won two Super Bowls with the Patriots though did not feature in either match.
However, because Garoppolo was on the Patriots’ roster for eight games last season, he was eligible for payments from the league based on the Patriots’ playoff performance; because the Patriots reached Super Bowl LII, he earned $107,000.