ST. LOUIS -- Rockies star third baseman Nolan Arenado is officially headed to the Cardinals in a six-player deal announced on Monday after a weekend of negotiation to nail down the particulars of a complicated blockbuster trade -- this offseason’s biggest.

St. Louis has had longstanding interest in the Gold Glove infielder, but it saw significant traction toward a deal over the last few days before being finalized in the late hours Monday.

• Arenado 'very thankful to be a Cardinal'

TRADE BREAKDOWN
Cardinals get: Nolan Arenado, cash considerations
Rockies get: LHP Austin Gomber, INF Elehuris Montero, RHP Tony Locey, INF Mateo Gil and RHP Jake Sommers

“Once I heard that it was done, I was thrilled,” Arenado said during his introductory press conference on Tuesday. “I'm very excited to join this team. It's a bittersweet moment, right? I'm going to miss some of the boys on the Rockies. ... But coming to a team like St. Louis with great players and great history, I'm just super excited. I've always admired this organization from afar. … I plan on staying here for a long time.”

Additionally, the Cardinals have agreed to restructure Arenado’s mega contract, adding a year onto the back end of the deal (making it run through 2027) with player opt-outs after the ’21 and ’22 seasons. Arenado will retain his no-trade clause, too, a source told MLB.com’s Mark Feinsand.

• 7 takeaways from Arenado trade

The Rockies will also send up to $51 million to the Cardinals to pay down Arenado’s salary, a source told Feinsand, but the particulars of how and when were not yet clear.

Heading to Colorado are left-hander Austin Gomber, who was expected to compete for a spot in the Cards’ 2021 rotation, infield prospects Elehuris Montero (St. Louis’ No. 8 prospect per MLB Pipeline) and Mateo Gil (No. 22), and right-handers Tony Locey (No. 19) and Jake Sommers.

“This was an opportunity we couldn’t pass up. And one that we had thought about for a while,” Cardinals chairman Bill DeWitt Jr. said. “... We always sort of dreamed that something like this could happen or might have happened, but when [Arenado] signed a long-term deal, obviously we didn’t think anything would come of it. But we’re always opportunistic in seeing players who can take our team to the next level, and I think we’ve demonstrated that over the years.”

News broke of the trade Friday night, but it took days to become finalized because of the complexities surrounding the amount of money being exchanged, Arenado needing to waive his no-trade clause with the Rockies and the renegotiation of the contract. Approval was needed from Major League Baseball and the MLB Players Association.

“I can tell you, like the last week or so, I kept feeling nauseous, like I just felt like something was going to go wrong,” Cardinals president of baseball ops John Mozeliak said. “... It just took a lot of patience on everyone's side to get it to where we are, and just grateful for everybody's participation to get a finish line.”

Arenado signed an eight-year, $260 million contract with the Rockies before the 2019 season. He's in line to make $35 million per year from 2021-24, then $32 million in '25 and $27 million in '26.

News of a deal came on the same day that the Cardinals finalized terms with starter Adam Wainwright, who signed a one-year contract for 2021 on Friday. The Cardinals also have an offer out to veteran catcher Yadier Molina, who has expressed his preference to return to St. Louis and could sign somewhere in the coming days.

Arenado, 29, has won a Gold Glove in each of his eight seasons with the Rockies and has been named a National League All-Star five times. He signed his extension in February 2019, but the team struggled out of the gate that season, frustrating Arenado and creating a path for a trade to St. Louis, a club that has been interested in the elite infielder for almost two years.

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In Arenado, the Cardinals are getting an infield complement to Paul Goldschmidt, another veteran slugger they acquired via trade in 2018. They also get an immediate boost to their offense -- the aspect of their game that has struggled and held them back for two years -- and protection for Goldschmidt in the lineup. Goldschmidt and Arenado will now combine talents that have totaled 11 All-Star appearances, 11 Gold Gloves and eight Silver Sluggers since 2013.

“When we were doing our due diligence on him, I think his reputation preceded him in the sense of how much he loves the game of baseball,” Mozeliak said. “... When I talk to other players about Nolan and what impresses them about him, it always came back to how hard he works, desire to learn, high baseball IQ. And those types of things are just very attractive to a team. And then knowing that he actually wants to be a part of the Cardinal organization I think is another key point, because you have a player that actually wants to be a part of something. It makes everything else that much better.”

Arenado missed time in 2020 with soreness in the A/C joint in his left shoulder and hit a career-low .253 with eight homers, but that was coming off a career-best .315 with 41 homers and 118 RBIs in 2019.

Potential starting lineup for the Cards

1. Tommy Edman, 2B
2. Paul DeJong, SS
3. Paul Goldschmidt, 1B
4. Nolan Arenado, 3B
5. Dylan Carlson, OF
6. Dexter Fowler, OF
7. Andrew Knizner, C
8. Harrison Bader, OF

(Matt Carpenter could potentially be used as a designated hitter and bat 6th or 7th. Also, Molina could potentially return to the team. In addition, Carlson could hit leadoff if Edman struggles there, and Tyler O’Neill could see time in the outfield or at DH.)

And the Cardinals got one of the best players in baseball without giving up on their future. For the trade to get done, the Cardinals were seeking salary relief, which they got in the Rockies sending cash, but they were hesitant to give up their top prospects with Arenado’s opt-out clauses. St. Louis didn’t have to include any of their most prized prospects -- Carlson (No. 1 in their system, according to MLB Pipeline), third baseman Nolan Gorman (No. 2), lefty Matthew Liberatore (No. 3) and lefty Zack Thompson (No. 5).

This trade is by far the biggest acquisition by an NL Central team this offseason and has put the Cardinals as clear favorites to win the division. The Cubs reportedly agreed to a deal with outfielder Joc Pederson on Friday, but only after sending starter Yu Darvish to the Padres in a trade that widens the gap between the top two NL West teams -- the Padres and Dodgers -- and the rest of that division, including the Rockies.

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For the Rockies, the trade completes the breakup of a relationship that quickly soured, and most likely completes the closing of a window that held so much promise in February 2019, when Arenado signed the eight-year deal. Colorado was coming off consecutive postseason appearances -- a first in the history of a team that began play in 1993.

But Arenado's signing further strained a payroll that was limited by a five-year, $70 million contract the Rockies signed Ian Desmond to before the 2018 season, and a six-year, $108 million extension for outfielder Charlie Blackmon signed at the start of the same season. That season ended with the Rockies coming closest to ending the Dodgers’ reign atop the NL West by forcing a Game 163 -- one the Rockies lost at Dodger Stadium.

“I got to know some of those coaches for a long time," Arenado said Tuesday, “and I've known a lot of them since I was 18 years old. I'm 29 now. Have some relationships that I'll cherish for the rest of my life out there.”

After the 2018 season, the Rockies declined to sign second baseman DJ LeMahieu and signed Daniel Murphy for the same two years and $24 million LeMahieu received from the Yankees. LeMahieu continued his stardom in the Bronx, while the Rockies turned in fourth-place finishes in 2019 and ’20. Throughout the contract, Murphy struggled with the bat and defensively after moving to first base. Last week, he announced his retirement.

Even more, the disappointment of 2019 led to offseason anger. In announcing that he was not making big moves at the Trade Deadline, general manager Jeff Bridich said a big part of the problem was the team’s main players were underachieving. Then, during the '19 Winter Meetings, Bridich said for the first time that he was listening to offers for Arenado from other teams. It seemed to be a settled issue when Bridich announced on Jan. 20, 2020, that there would be no deal. But that same night, Arenado responded to MLB.com.

“There’s a lot of disrespect from people there that I don’t want to be a part of,” Arenado said in a text. “You can quote that.”

So in 2020, the relationship with Arenado was already sour. Desmond elected not to play after the pandemic shutdown, and Murphy lost his starting position. Trying to capitalize on the ’17 postseason trip, the Rockies signed relievers Wade Davis, Jake McGee and Bryan Shaw to contracts totaling $106 million; however, McGee and Shaw were released before the season started, and Davis spent much of the year injured and was released near the end.

After another rough Rockies season and, finally, the trade with the Cardinals, the Rockies find themselves at a crossroads.

Unloading Arenado and not receiving immediate help for the lineup or bullpen, both of which struggled in 2020, can logically be read as a signal that the Rockies are rebuilding. They're seen as clearly behind the two top teams in the NL West -- the World Series champion Dodgers and a Padres club that became a contender in '20.

Does Colorado also look for takers for star shortstop Trevor Story and, to a lesser extent, right-handed pitcher Jon Gray and righty reliever Mychal Givens (all in their contract year), for a greater bevvy of prospects? The Arenado trade increased the Cards’ future payroll. The Cards, as a result, weren't inclined to give up top-drawer prospects.

Or do the Rockies, who like their starting pitching, look for veterans under short-term deals to prop up the lineup and bullpen, attempt to make a playoff run, then reassess at the Trade Deadline?

The Cardinals and Rockies have a limited trade history, but they have engaged in many talks throughout the years. Two notable deals stick out: After the 1999 season, the Rockies traded pitcher Darryl Kile to the Cardinals, and in 2004, the Rockies traded future Hall of Famer Larry Walker to St. Louis, a deal that helped the Cardinals to the World Series. Matt Holliday was also a former Rockie who found a home in St. Louis, although he took a detour through Oakland first.

Now Arenado has joined that list.