"I'm just going to speak from my heart. I wish we were standing here in different circumstances," Karlsson said in Ottawa. "It's a very emotional and sad day for me and my family, but it's an unfortunate part of the business.
"... At the same time I also want to thank the San Jose Sharks for everything that they have done to acquire me. It showed a lot in how much they wanted me to be part of their organization and their team, and for that, I'm very grateful. I'm going to be extremely excited once I get there. And I'm looking forward to whatever is ahead of me."
Ottawa received forwards Chris Tierney and Rudolfs Balcers, defenseman Dylan DeMelo, the rights to unsigned forward Joshua Norris, a first-round pick in the 2019 NHL Draft or 2020 NHL Draft, a second-round pick in the 2019 draft, and two conditional draft picks.
[RELATED: Erik Karlsson career timeline | 2018-19 NHL Trade Tracker | Fantasy spin: Karlsson trade to Sharks]
The Sharks also acquired forward Francis Perron in the trade.
Ottawa offered Karlsson, a 28-year-old defenseman, a contract extension July 1, the first day it could do so, but he would not re-sign with the Senators. The Tampa Bay Lightning and Dallas Stars each reportedly made trade offers to Ottawa in early July.
"I haven't really still wrapped my mind around what is really going on," Karlsson said. "I think it's been happening really fast, even though there's been a lot of noise for almost a year now. But again, I never, in my wildest imagination, ever thought that I was going to leave this place."
Video: Senators trade Erik Karlsson to the San Jose Sharks
San Jose has not announced a new contract for Karlsson, who said, "As for right now, that's a private discussion and not something that I'm going to elaborate on."
Karlsson had 62 points (nine goals, 53 assists) in 71 games for the Senators last season. He led Ottawa in points, or tied for the lead, each of the past five seasons.
"We actually started the process last year at the [NHL] Trade Deadline," Sharks general manager Doug Wilson said. "It just kind of went from there. You always try and keep involved in these types of opportunities, because it's really rare that this level of difference-maker becomes available and you always want to be involved in that. It picked up steam probably the last two, three weeks, but it was never really off the burner because it was something that you always want to be involved in."
Ottawa owner Eugene Melnyk, in an open letter to fans published Monday, introduced the concept of a multiyear rebuilding plan to improve on and off the ice. It did not address the possibility of trading Karlsson. The Senators opened training camp Thursday.
"I think that they made it very clear in what direction they're going with," Karlsson said. "Unfortunately, I wasn't part of that and I respect that. That's their decision. And I wish them nothing but the best. I think that they're going to do wonderful things here. They have a good group of guys down there that are extremely motivated to keep pushing forward and doing whatever they have to do to be successful, not only this year, but for a long time. I was not part of that plan, that's why we are standing here today, and from my point of view, that's sad, I never wanted to leave this place. But at the same time, I respect their decision, that's their decision to make, and I wish them nothing but the best, and I know they're going to do great because the group of guys that they have down there are doing everything they possibly can to be as successful as they possibly can."
The Senators (25-45-12) finished 15th in the Eastern Conference last season, 30 points behind the New Jersey Devils for the second wild card into the Stanley Cup Playoffs, one season after losing to the Pittsburgh Penguins in overtime in Game 7 of the Eastern Conference Final.
The captain of the Senators since 2014, Karlsson is a two-time Norris Trophy winner (2012, 2015) and finished second in 2016 and 2017. Selected by the Senators in the first round (No. 15) of the 2008 NHL Draft, Karlsson has 518 points (126 goals, 392 assists) in 627 regular-season games and 37 points (six goals, 31 assists) in 48 games in the Stanley Cup Playoffs.
"Erik Karlsson was probably going to gather the best return in a possible rebuild," Ottawa general manager Pierre Dorion said. "This was not an easy situation for us, to trade a player of Erik Karlsson's caliber. But for us to be where we need to be for the long term in this rebuild, we had to make this decision at this point in time."
Karlsson has 355 points (83 goals, 272 assists) in five seasons since returning from a torn Achilles tendon. Among NHL defensemen, only Brent Burns of the Sharks, with 326 points (107 goals, 219 assists), has more than 275 in that span.
"Ultimately, to acquire a player like this, you have to give to get and we are losing some quality players but also some very good people," Wilson said. "All of the players leaving our organization have a very bright future in this league."
Tierney, 24, set NHL career highs in points (40), goals (17) and assists (23) last season, his fourth in the NHL, and had two assists in 10 playoff games. He has 104 points (41 goals, 63 assists) in 284 NHL games with the Sharks, and 12 points (five goals, seven assists) in 40 playoff games. Tierney was San Jose's second-round pick (No. 55) in the 2012 NHL Draft and signed a two-year contract with the Sharks on July 18.
DeMelo, 25, had 20 assists in 63 games last season and one assist in 10 playoff games. He was San Jose's sixth-round pick (No. 179) in the 2011 NHL Draft and has 32 points (three goals, 29 assists) in 133 NHL games.
Balcers, 21, played last season for San Jose of the American Hockey League and had 48 points (23 goals, 25 assists) in 67 games. He was selected by the Sharks in the fifth round (No. 142) of the 2015 NHL Draft.
Norris, 19, was the No. 19 pick in the 2017 NHL Draft. He had 23 points (eight goals, 15 assists) in 37 games at the University of Michigan last season.
"We've told our fans what we started by telling you yesterday: Right now, we're in a rebuild," Dorion said. "We want to be a Cup contending team year after year. We just don't want to have the inconsistencies that we've had in the past 10 years of making the playoffs, not making the playoffs. Erik Karlsson, for what it seemed like, was probably going to be here for just another year. What we did here today was make sure that our rebuild was going to be as successful as possible."
Perron, a 22-year-old forward, was a seventh-round pick (No. 190) by Ottawa in the 2014 NHL Draft. He had 15 points (four goals, 11 assists) for Belleville of the AHL in 2017-18.
The Sharks reportedly were one of the teams to meet with free agent forward John Tavares before he signed with the Toronto Maple Leafs.
"We were looking for a difference-maker, and there's really probably two main ones, both John and Erik, in the last little while," Wilson said. "We kind of kept our powder dry hoping that this type of opportunity would come to fruition, and it did. It doesn't always happen that way. Sometimes you've got to wait a little bit more time, but I think the timeline that Ottawa was operating under was prior to the season, and it worked well for us. To me, it's great to get [Erik] in sooner than later so he can integrate in with our group."
Ottawa receives San Jose's first-round choice in either 2019 or 2020 (not lottery protected); if the Sharks miss the playoffs this season it will be a 2019 selection, otherwise it will be in 2020.
The 2019 second-round pick Ottawa receives from San Jose will be the higher of the two picks the Sharks own, the Florida Panthers' and theirs.
Should San Jose sign Karlsson to a contract, Ottawa will receive the Sharks' second-round selection in 2021, which would upgrade to a first-round selection (not lottery protected) if San Jose reaches the Stanley Cup Final this season.
If Karlsson is on an Eastern Conference roster (reserve list) this season, the Senators will receive an additional first-round pick from the Sharks no later than 2022.
"I think that once it settles down here a little bit, you can start looking ahead and moving forward a bit, but as of right now, it's extremely emotional and a sad moment," Karlsson said. "Even though you've heard a lot of things about that this could be possible, I think that you can't really prepare for anything. It's sad."
NHL.com columnist Nicholas J. Cotsonika and correspondent Callum Fraser contributed to this report.