In two separate goalkeeping howlers, keeper Karius first attempted to throw the ball out only for it to hit Real Madrid's Karim Benzema, who scored.
He went on to fumble an effort on goal by Gareth Bale, which also found the back of the net as Liverpool slumped to a 3-1 defeat.
The squad touched down at Liverpool's John Lennon airport this morning, with a dejected looking Karius stepping off the plane with his teammates.
After the match he apologised to fans who went on to bombard him with vile criticism for the string of errors.
Karius told talkSport: "I don't feel anything right now. Today I lost my team the game.
"I feel sorry for everyone. I'm so sorry for everyone, for the team, for the whole club. The mistake cost us dearly."
"If I could go back in time I would.
"I just feel sorry for my team. I know I let them down today.
"For now, I'm just really sorry for everyone that those goals cost us the title basically."
He was sent death threats on Twitter by some fans. One wrote online: "Get out of our club or die."
Another wrote: "My Liverpool boys fought hard and I'm proud of them. Except for Karius he can die in a hole."
After the match Karius said: "'If I could go back in time, I would. I feel sorry for my team. I know I let them down."
Footballers and other fans however leapt to the defence of the 24-year-old.
German footballer Jerome Boateng tweeted a message of support for Karius. He wrote: "Stay strong and keep your head up Loris Karius. We all make mistakes!"
Inter Milan sent a message of support to him on the team's official Twitter page: "A bad night can happen to anyone, other successes are waiting for you in life! A hug from all of us at #FCIM"
Italian side Napoli also sent him a message of support: "Chin up, @LorisKarius. Anyone can have a bad game."
Independent Liverpool supporters' site Rousing the Kop posted online: "If we believe in what You Never Walk alone stands for, then supporting, not abusing, Loris Karius is what we need to do."
One fan posted: "'The people who are tweeting Loris Karius saying they hope he dies are not Liverpool fans; they are disgusting human beings."
There was further disaster for Liverpool as their talismanic striker Mohammed Salah was forced off with a dislocated shoulder.
Former Champions League winner Paul Scholes, who won the competition twice with Manchester United, said Liverpool manager Jurgen Klopp will be 'desperate' to recruit a new first choice goalkeeper after last night's performance.
"I think Liverpool know that they needed to strengthen the goalkeeping position anyway. I think they've know that for quite some time," said Scholes speaking at an official Uefa Champions League Final viewing party at London's Sky Garden.
"Will this speed up the process? You'd have to think so. I think they'll be desperate for a goalkeeper.
"I know he (Klopp) has shown faith in Karius but I don't think he's of the quality needed if you're going to win the Champions League, if you're going to win a Premier League.
"We always found in our teams, we needed a top goalkeeper, there's no doubt about that, and I think Liverpool are the same."
Former Liverpool goalkeeper Ray Clemence said Karius will have to live with his mistakes "for the rest of his life."