"It was a major disappointment," said Dean. "Mainly because I always felt that we would get there. I thought we had a squad that was capable, we've played some really good football over the season.
"I think the disappointment was probably magnified by the fact that we hadn't played well and there's not many times you can say that during this season. It was a big disappointment to fall at that stage, especially how we started the game last week.
"They scored a freak goal that was deflected and it was just how we reacted to that goal. It gave us a bit of a kick in the teeth and we went chasing a game we didn't need to chase, we just needed to keep doing what we were doing. Unfortunately it put pay to our Play-Off hopes."
This weekend Dean wants his side to finish on a high.
"It would be nice to," Dean agreed. "I've got memories of last season against Blackburn where we didn't play very well and I was certainly very aggrieved with the players. On the other side of that, the season before we beat Huddersfield away 5-1. We've got to be good, we've got to be professional.
"We've got a couple of injuries at the moment. Romaine Sawyers came off with an ankle injury and Florian Jozefzoon's got a knee injury as well so they are doubtful for the game. I've got options to change it up again as well because there are a number of players who have played a lot of games. It certainly gives me the opportunity to look at a few who, in my opinion, wouldn't weaken us."
Dean was asked how it will feel to see out the 2017/18 season in front of the home fans at Griffin Park on Sunday. He pointed out that there are still targets to hit.
"There's an opportunity for us to finish seventh and get 71 points," said Dean. "That's something that I've passed on to the players already. We've taken a lot of plaudits from our supporters this season for the way we've played and we're very thankful for their support, especially after the start we had. It would be nice to go out on a high note this season in front of the home fans and give them something to shout about."
Regardless of the result on Sunday, Brentford have already secured their fourth consecutive top ten finish in the Sky Bet Championship. Asked about this being a testament to his squad, Dean said: "It certainly is, and the Club. The Club in general has become an established Championship team. Four years in the top ten or eleven shows that it isn't a team that's just fighting to survive.
"We've gone through that survival stage, if there ever was that stage in the Championship for us, and we're an established team that likes to be pushing at the top end.
We asked Dean what he was expecting from his team on the final day of the season.
"I want to see a top performance to be honest," said Dean. "Hull have been free scoring of late. They had that 5-5 game with Bristol City on their travels, they beat Burton 5-0 and QPR 4-0 so they've certainly got goals within the team.
"One of the things that I've said to the players is that we have to be very good without the ball on Sunday. I feel that we've got enough with the ball to hurt most teams in this league so if we get the without the ball part right then we will be alright."