On Monday, that speculation was resolved as the Blues dealt Shattenkirk and goalie Pheonix Copley to the Washington Capitals in exchange for a first-round pick in 2017, a conditional second-round pick and forwards Zach Sanford and Brad Malone.

ST. LOUIS - For several months or more, Kevin Shattenkirk's name had been the subject of constant trade speculation.

Shattenkirk would have become an unrestricted free agent at the end of the season if he wasn't signed before July 1.

"It was a difficult decision," General Manager Doug Armstrong told stlouisblues.com. "Kevin has been a big part of our success the last seven years, not only on the ice, but off the ice. (I have) a lot of respect for Kevin as a player and a person. I wish him nothing but the best.

"This really started last year at the entry draft," Armstrong added. "I went to Kevin and we talked about a potential extension, and he was available for one on July 1, an eight-year extension. He just felt at that time he needed a different challenge and he wanted to test free agency, so the ball started rolling on different scenarios of a sign-and-trade, or a trade at last year's entry draft. That didn't happen and we were in no rush to make it happen... We got to the trade deadline (this year), our team was in a precarious playoff spot and it just felt with where we are and where we need to go, it was time to make a move.

"We talked to all the teams and we wanted to acquire multiple assets, a player we are excited about. We were able to do that."

Video: Armstrong breaks down Shattenkirk trade

In addition to the first-round pick and the conditional pick, the Blues acquired a big center in Sanford, who made his NHL debut earlier this season. Sanford was expected to return to Boston College this season but played so well at training camp, the Capitals offered him a spot on their NHL roster on for opening night. He was eventually reassigned to their AHL affiliate - the Hersey Bears - before being recalled again due to an injury to forward Andre Burakovsky. He recorded his first NHL goal on Feb. 11, which eventually was a game-winner.

The 22-year-old Salem, Massachusetts native scored 39 points (13 goals, 26 assists) in 41 games with Boston College last season, where he led the team in assists, ranked third in points and fifth in goals as a sophomore.

"(Our scouts) see a lot of Tage Thompson in him, a player we took in the first round (in 2016)," Armstrong said. "Big body, a point-per-game player as a sophomore at Boston College. I see a big player that's multi-positional. We're hoping to see him as a centerman, a player than can produce offense. You hope everything works out perfectly, but if (we have) a 6-foot-4 Zach and a 6-foot-4 Tage Thompson down the middle for a few years, it wouldn't hurt my feelings."

"Everything I've heard has been a real positive," Blues Head Coach Mike Yeo said of Sanford. "It sounds like a real exciting piece for the future… I'm excited to have him."

Malone, 27, will report to the Chicago Wolves. He has played in 52 games for the Hershey Bears this season, tallying 20 points (seven goals, 13 assists) and 66 penalty minutes. Like Copley, he could become an unrestricted free agent after the season.

"We got a deal that we were comfortable with and moved forward," Armstrong said. "If this team was at the same place it was a year ago, Kevin Shattenkirk would be a St. Louis Blue. We're not in the business of trading good players for prospects when your team has a chance to win the Cup. Now, this team has to get (in the playoffs) on their own, and obviously it's going to be more difficult.

"If we can get in, you always have a chance to win. You never know once you get in what can happen."

Video: Armstrong holds press conference on Shattenkirk trade