Barca were in the box seat heading into the Champions League semi-final second leg as they lead 3-0 from the first leg at the Nou Camp, and only few gave Liverpool a chance.
However, Liverpool went ahead after just seven minutes through Divock Origi and kicked on in the second half, when substitute Georginio Wijnaldum's quickfire brace was followed by Origi notching from a quick corner to seal a 4-0 win and progress 4-3 on aggregate.
It is the second time in as many seasons that Barca have crashed out after squandering a three-goal advantage.
They lost 3-0 to Roma in last season's quarter-finals, having lead 4-1, to go out on away goals.
"The most painful thing is to repeat [what happened in Rome]," he said. "It happened last season and it has happened again.
"It was a different game (to last year). Liverpool had a brilliant start, we concede the first goal quickly but we reacted well and had chances to score.
"We got into their box in dangerous positions but we didn't take those chances. When you lose 4-0 you can't have any excuses. They were better than us and we have to accept it.
"We're really sorry to the fans, we all play; everything that we do is to make the fans happy, to make them proud of us. Everyone expects us to win all the time but we have lost and in a very painful way.
"This is the first game we have lost in the Champions League this season but we are out. The players are the ones that play on the pitch, they are hurting more than anyone."