An emotional Anthony Joshua choked back tears after losing his heavyweight world title rematch with Oleksandr Usyk in Saudi Arabia on Saturday.
The Briton, 32, was defeated by split decision, having also lost to the Ukrainian on points last September.
When asked about his performance at a post-fight news conference, Joshua said: "It's really, really hard for me to say I'm proud of myself.
"I'm upset, really, deep down in my heart."
The two-time world champion then covered his face with both hands, taking deep breaths, as his promoter Eddie Hearn took the next question.
Joshua, who won super-heavyweight Olympic gold at London 2012, won his first 22 professional fights but has now lost three of his past five contests, all of them for world titles.
He said the pressure and intrusion he faces "comes at a cost", adding "it will never break me but it takes real strength not to break me and there is a little crack in the armour because that took a lot".
'When you're angry you do stupid things' Joshua lost his temper moments after Usyk had been declared the winner - dropping two of the champion's belts over the top rope of the ring and then arguing with the opposing team.
"When you try and do things from your heart, not everyone is going to understand," Joshua explained.
"It was just from the heart. I knew I was mad at myself. Not at anyone, just myself. I was like I got to get out of here because I'm mad.
"When you're angry you might do stupid things. Then I realized this is sport. I came back and did the right thing."
On the incident, Usyk said: "I feel nothing but respect for AJ.
"I saw him a bit emotional and like bullying some of my teammates. That would be a bare-knuckle fight that I don't recommend him to do because most of them are horrible street fighters."
Joshua's promoter Hearn gave a passionate defence of his fighter.
"This is someone who I want my kids to look up to," he said.
"If he's out in public, he gives everyone his time. He's one of the nicest guys. He's a competitor and winner.
"What you saw was raw emotion. A real person who wanted to win badly."
Hearn dismissed any suggestions of Joshua retiring, saying he would like to see him be more active. He wants Joshua to return in December and have at least three fights in 2023.
Joshua has fought just twice - both against Usyk - in the last two and a half years.
"I'm a fighter for life. That hunger never dies. Fighter for life," Joshua said.
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