The Athletic and Stadium's Shams Charania explained how Irving and Tatum, both of whom played at Duke, built a relationship as the latter was entering the NBA in 2017. The bond strengthened during their two years as teammates.
"Ky is like my big brother," Tatum said. "We still talk to this day, and we've talked a few times this playoffs. He always encourages me to be special. Having that relationship with him and having somebody like him in my ear at a young age, it means a lot."
Irving isn't the only star on whom Tatum leaned to improve his game. ESPN's Tim Bontemps reported in October 2019 how he had worked with Kobe Bryant and developed habits the Celtics were attempting to counteract.
Fans in Boston probably don't remember Irving's time there too fondly, and the six-time All-Star didn't appear to mesh with the Celtics' young roster. Terry Rozier spoke about some of those problems during an appearance on ESPN's Get Up! last May.
Irving clearly made a positive impact in some respects, though.
His arrival was supposed to put Boston over the hump in the Eastern Conference title race. His departure may have actually set that in motion.
With Irving gone, Tatum is the team's go-to option on offense. Perhaps not coincidentally, the 22-year-old enjoyed a career year during the regular season. He averaged 23.4 points and 7.0 rebounds while shooting 45.0 percent from the field and 40.3 percent from beyond the arc.
The Celtics also have a 2-0 series lead on the Toronto Raptors in the conference semifinals, easing some doubts about their direction with Tatum as the cornerstone.