Goals from Ivan Toney, Vitaly Janelt and Marcus Forss eventually booked the Bees a trip to Wembley, where they will face either Swansea or Barnsley for a place in the Premier League.
Trailing 1-0 from the first-leg, the Bees got off to a nightmare start when they were caught on the break from their own corner, allowing Arnaut Danjuma to open the scoring.
“I smashed my foot into the ice cooler after the 1-0 goal,” Frank said afterwards. “Then I thought, ‘No, keep your head’.
“Then, five seconds later, I smashed my foot into the bin next to it!”
The Bees recovered, however, with Toney converting from the penalty spot before Bournemouth were reduced to 10 men when former Brentford man Chris Mepham was sent off for a rugby-style tap-tackle on a clean-through Bryan Mbuemo.
Janelt then levelled the tie on aggregate shortly after the break before Forss won it late on.
“What a rollercoaster of emotions,” Frank said. “Only sport and especially football can do that. I’m not talking about only us, I’m talking about everyone involved in Brentford and everyone involved in Bournemouth.
“We started fantastically, right from the off, aggressive, on top of the game, we won a corner, and then a split-second later it’s down in the back of our own net.
“But the resilience and attitude from the players was that we were bang on it.”
The game was played in front of more than 4,000 fans at the Brentford Community Stadium, many of whom will have been attending a match at the club’s new home for the first time, having been shut out by Covid restrictions for the majority of the year since the move from Griffin Park.
“We have achieved something,” Frank added. “I think it’s big, to go to the Play-Off Final. Of course we know the ultimate one is to win on Saturday. But we know very well that there is a long, long way until we hopefully cross the goalline but it is a massive achievement, to get to the Play-Off Final two years in a row.
“After the third goal, you heard the fans singing and it was emotional, you wanted almost to cry a bit.
“I said to the players before the game that we needed a top performance but the message was also to the fans that we needed a top performance from them and we definitely got it.
“It was 4,000 and it felt like 40,000. I can’t wait to see a full stadium - the roof will fly off. If I should edge it between the players and the fans for the top performance, I’d go for the fans.”