Anthony Joshua has said he let himself down in the moments after his split decision defeat in a rematch with Oleksandr Usyk on Saturday.
Joshua failed to reclaim the WBA, WBO, IBF and IBO heavyweight titles as he suffered his second straight loss to Usyk -- his third defeat in his last five fights. The 32-year-old threw two of Usyk's belts to the floor after the final bell before storming out of the ring, only to return later and deliver an impassioned speech.
"I wish Usyk continued success in your quest for greatness. You are a class act champ" Joshua said in a Twitter post on Sunday.
"Yesterday I had to mentally take myself into a dark place to compete for the championship belts! I had two fights, one with Usyk and one with my emotions and both got the better of me.
"I'll be the first to admit, I let my self down. I acted out of pure passion and emotion and when not controlled it ain't great. I love this sport so so much and I'll be better from this point on."
The 32-year-old also reflected on his behaviour during his post-fight news conference, saying his speech, in which he called himself a new breed of heavyweight and led a cheer for Usyk, was "from the heart."
"When you try and do things from your heart, not everyone is going to understand," Joshua said. "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 here because I'm mad.
"When you're angry you might do stupid things. Then I realised this is sport. I came back and did the right thing."
Joshua fought back tears after the bout as he reflected on his defeat, saying he was deeply "upset" with his performance against the Ukrainian heavyweight champion.
"It's really, really hard for me to say I'm proud of myself. I'm upset, really, deep down in my heart," he added.
"I tried a different style... in the last fight I wanted to compete as a boxer, but it wasn't good enough, and tonight wasn't good enough."
Joshua said he plans to return to the ring in December, adding that his promoter, Eddie Hearn, wants him to have three or four fights next year.
"I spoke to Eddie and asked him if it's possible to get out in November because momentum is important in boxing. Eddie said December," Joshua said.
"If it's about who I fight, it's come one, come all. Whoever wants it can get it, I don't mind."
Information from Reuters contributed to this story.