Kim Hellberg said the 'Spygate' saga that overshadowed his Middlesbrough side's Championship play-off semi-final defeat to Southampton was "disgraceful" and "breaks my heart".
It is alleged a member of Southampton staff was caught trying to observe a Middlesbrough training session last Thursday.
After a goalless draw in the first leg on Saturday, Shea Charles' 116th-minute winner earned Saints a 2-1 aggregate win and a place in the play-off final at Wembley on Saturday May 23.
"I worked 15 years as a coach, trying to get to the Premier League. That's my dream for 15 years," he said in his post-match press conference.
"I know there are clubs with bigger resources or parachute payments that can spend more money. There are teams that have bigger squads than us, teams that have more money to spend.
"What you have as a coach and a group is the tactical element of the game where we can beat the opponent and I think that's what everyone loves about the game. That's why I look at England and think it's the home of football, where I want to be, what I'm dreaming about. You're so proud of your football and I think that's absolutely amazing, that's why I wanted to be here.
"When you have more money and all those things, you try to find a way to get an advantage, that's the way I try to go with my team. That's what you always try to do, because we can be better in that element.
"Alex Neil said a very good thing after the (Millwall) game. He said 'I think I let people down as we haven't won'. In that way, he said he had let people down. That's often the feeling a coach goes home with because you think, what I could control was the tactical aspect of the game or helping my players more.
"When you have done that and, for a week or two weeks up to this game, put every second away from your family to watch Southampton every game you can to try to gain the advantage that we can actually get, if we wouldn't have caught that man they sent up on a five-hour drive, you would sit there and say, well done, maybe, in the tactical aspect of the game and I would go home and feel like I had failed in that aspect I had to help my players with.
"When that is taken away from you in that way, when someone decides: 'No, we're not going to watch every game. We'll send someone instead and film the session and see everything and hope we don't get caught'. I guess that was why they were switching clothes and all those things.
"It breaks my heart in terms of all those things I believe in. That's the thing.
"I don't care if there are other rules in different countries. This is England where football is the biggest thing.
"That's my feelings about it. I think it's disgraceful. It makes me very sad."
Asked if he believed Tonda Eckert knew of the alleged 'spying', Hellberg said, simply: "I cannot answer. No comment."
Meanwhile, Southampton head coach Tonda Eckert walked out of Saturday's post-match press conference after being pressed on 'Spygate'.
And he walked out once again on Tuesday night when the second question of the press conference was: "Are you a cheat?"
The press officer who accompanied him swiftly shut it down and told the journalist in question to "show some respect".
A disciplinary hearing before the final has been recommended by the EFL given the "nature of the matter" and anything could still happen in spite of Tuesday night's outcome.
The statement from Southampton's chief executive on Tuesday asked for time to conduct an internal review, but the decision on a hearing will be made by the Independent Disciplinary Commission.
Although 'spying' has happened before in 2019, there were no explicit rules against it at the time and Leeds were punished on the 'good faith' law. That law still exists plus there is now rule 127 which outlaws spying within 72 hours of a game.
In that sense this is the first time this law has been truly tested, and every type of punishment is at the disposal of the Independent Disciplinary Commission.
It is fair to say Boro believe Southampton have plainly "cheated" and the club want the most severe punishment available - and a sporting one. Boro's view is that a fine would serve little purpose.
Before Tuesday's game, Southampton asked to be given time to conduct an internal review into the circumstances surrounding the 'spygate' scandal.
The club were charged on Friday by the EFL, who asked an independent disciplinary commission to shorten the response period from the usual 14 days and to list a hearing "at the earliest opportunity".
Southampton chief executive Phil Parsons told the club's official website: "The club is fully co-operating with the EFL and the disciplinary commission, whilst also undertaking an internal review to ensure that all facts and context are properly understood.
"Given the intensity of the fixture schedule and the short turnaround between matches, we have requested time to complete that process thoroughly and responsibly.
"We understand the discussion and speculation that has followed over recent days, but we also believe it is important that the full context is established before conclusions are drawn."
