The NBA's first blockbuster trade of the summer occurred on Friday, with ESPN's Adrian Wojnarowski reporting the Boston Celtics will send Kemba Walker, the No. 16 overall pick in the 2021 NBA draft and a 2025 second-rounder to the Oklahoma City Thunder for Al Horford, Moses Brown and a 2023 second-round pick. 

Wojnarowski added the deal will give Boston financial flexibility to potentially make more moves this offseason by getting off of the $73 million still owed to Walker. 

The Thunder figure to be the most prominent team mentioned during the draft on July 29. They now have three first-round picks, including their own still-to-be determined lottery choice and the No. 18 selection from the Miami Heat. 

Per ESPN's Jonathan Wasserman, Oklahoma City could end up with a fourth first-rounder and up to seven total picks in this year's draft:

Updated Celtics Depth Chart

PG: Marcus Smart, Payton Pritchard, Tremont Waters

SG: Evan Fournier (eligible for unrestricted free agency), Romeo Langford

SF: Jaylen Brown, Aaron Nesmith

PF: Jayson Tatum, Grant Williams, Semi Ojeleye (eligible for unrestricted free agency), Jabari Parker (team option for 2021-22)

C: Al Horford, Tristan Thompson, Robert Williams, Luke Kornet (eligible for unrestricted free agency), Moses Brown

Updated Thunder Depth Chart

PG: Kemba Walker, Theo Maledon, Ty Jerome

SG: Shai Gilgeous-Alexander, Svi Mykhailiuk (eligible for restricted free agency)

SF: Luguentz Dort, Kenrich Williams, Gabriel Deck

PF: Darius Bazley, Aleksej Pokusevski, Jaylen Hoard (eligible for restricted free agency), Josh Hall (eligible for restricted free agency)

C: Isaiah Roby, Tony Bradley (eligible for restricted free agency), Mike Muscala (eligible for free agency)

Rosters via RealGM.com 

One of the many offseason storylines for the Celtics was about their relationship with Walker. 

B/R's Farbod Esnaashari reported on June 9 that the two sides wanted to go their separate ways after two seasons together. 

A series of knee problems that began late in the 2019-20 season seemed to impact Walker's performance on the court. He missed the first 11 games this season after undergoing treatment and a stem cell injection in December. 

Walker did average 19.3 points per game in 43 starts this season, but his 42.0 field-goal percentage was his worst since 2014-15. 

The Thunder might not end up being the final stop for Walker this offseason. They are taking a long-term approach to team building, so paying a 31-year-old point guard $36 million in 2021-22 and possibly $37.7 million in 2022-23 if he picks up his player option wouldn't seem to make much sense. 

The Celtics did have to sacrifice a first-round pick this year, but B/R's Jonathan Wasserman noted there is a talent drop off after the top of the lottery this year that suggests they won't necessarily miss that selection.

Horford gets to go back to a Boston franchise that he knows well and had great success with from 2016-19. He averaged 13.5 points, 7.0 rebounds and 4.6 per game in 208 starts for the Celtics. The five-time All-Star shot 38.2 percent from three-point range with the team. 

It should also help the Celtics that Horford already has experience playing alongside Jayson Tatum and Jaylen Brown, thus they shouldn't need much time to develop chemistry on the court. 

The acquisition of Brown in the deal could make Tristan Thompson expendable. Brown played well with 8.6 points and 8.9 rebounds per game in 43 appearances for the Thunder in 2020-21. His offensive rebound average was slightly higher than Thompson's (3.6 to 3.1). 

Thompson's $9.72 million salary next season isn't small, but it's hardly an impossible-to-move contract. 

There's still work for the Celtics to do in order to make themselves a title contender in the Eastern Conference, but their first move of the offseason has them on the right track.