When it comes to Boston Celtics rookie small forward Jayson Tatum, the 20-year-old rising star put together quite an amazing first season in the NBA after being selected No. 3 overall in the 2017 NBA Draft out of basketball powerhouse Duke University.

Tatum's former teammate in four-year shooting guard Grayson Allen, who is expected to be selected in the 2018 NBA Draft, said he knew immediately that Tatum would succeed at such a high level in the NBA.

However, Allen admits that he just didn't expect it to happen so quickly with Tatum.

“I knew he was gonna perform really well,” Allen said of Tatum, via a tweet on Friday afternoon from Celtics writer Jared Weiss of The Athletic. “Maybe not this soon, but I knew he was gonna do really well. It was amazing to see. He’s always had that clutch, that want-to-be-in-the-moment in him and that’s why he thrived in the playoffs.”

Back in 2016-17 at Duke while Allen was in his junior season and Tatum was a standout freshman, Allen reminisced on Friday with members of the media about how dominant of a player Tatum was when he had to be guarded one-on-one during practice.

Allen did say that there was only one player on Duke's roster at the time that was able to best Tatum one-on-one: former Blue Devils power forward Amile Jefferson, who went undrafted in 2017 and is now a member of the Minnesota Timberwolves organization.

“[Him] beating us one-on-one every day since the summer when he got there, although there is a little asterisk to that,” Allen said of Tatum. “You might have to ask [him] about this, but I don’t know if he ever beat Amile one-on-one. But I think that’s from Amile’s side of the story.”

It will be very interesting to see how much more Tatum develops at such a young age during his second season in the NBA, especially when the Celtics get two of their star players back healthy in Kyrie Irving and Gordon Hayward to help Tatum become even better on the court.