Anthony Joshua has admitted he needed to "make changes" after losing comprehensively to Oleksandr Usyk in his last outing.
The former world heavyweight champion was heavily favoured to beat former cruiserweight champion Usyk when they fought in September, but was comfortably beaten at the Tottenham Hotspur Stadium.
He immediately exercised his rematch clause to get a rematch with the Ukrainian, and will likely face him in the early part of next year despite recent talk of a step aside deal to let Usyk face Tyson Fury for the undisputed title.
"I had to make changes," Joshua admitted during an interview with the BBC. "If you remain the same, you get the same results.
"I've got to look at myself, I can only be accountable for me. I'm angry at myself and the only way I can be in a better place is to get myself right by going out there and performing.
And Joshua has said that his anger won't go away for a number of months, likely until he has faced Usyk again and reclaimed the world titles.
He says that he will continue to put on a brave front to the public, but insists that he will be working hard in the gym to make sure he puts in an improved performance in the rematch.
"It's going to be like this for a few months," Joshua continued.
"I do things with a smile on my face, but behind that there's a lot of tension brewing and the only way to get it out is by training and performing."
And he has promised to perform better in the second bout with Usyk, after losing by unanimous decision to the unbeaten former Olympic gold medalist.
Usyk is a fantastic technical boxer, but it is believed that he is very small for heavyweight, and could be beaten by Joshua or Fury if they use their size to the fullest.
"I know I can be better than that night," he explained.
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"It's easier to say than it is to do, but within my heart and soul, my brain and body, I truly feel I've got a lot more to give.
"I'm angry. It's growing, but it's fuelling me every day.
"I think people still recognise me as champion, even though I haven't got the belts round my waist.
"They know I've got the capability of becoming champion."
There have been rumours that Joshua may be willing to take a substantial amount of money to allow Fury to fight Usyk, but that appears to be fanciful, with the Watford native training hard for his rematch.
Joshua told iFL TV last week that he would be willing to entertain such a deal if it were right for his legacy, but there is no official offer from Fury's side as yet.
He has also recently met with coaches in America as he contemplates a possible change in trainer, although it seems that he would rather stick with head coach Rob McCracken if possible.
