Johnson returned with match figures of three for 200 from 38.4 overs in the second Test which Australia lost by 115 run to England.

"I guess it (poor form) started off with the personal side of things. That really probably did get to me. I was probably denying it as well at the time. The personal things that came out, it was mostly through Lord's where I felt that pressure," Johnson was quoted as saying by the Herald Sun.

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"Mentally, I have learnt to be a lot stronger. I've just got to concentrate on what I'm doing out in the middle," Johnson said.

"This is what I have to do for a living and I've just got to leave everything behind me when I'm out there. My problems got technical as well because I was thinking about it but in the end it was just more of a mental thing."

The 28-year-old Queenslander said the emotional toll caused by his mother Harber's claim that the pacer was "stolen" from her by his fiancee Bratich had such an adverse affect on him that he completely lost his focus on bowling.

"I just had to concentrate on where I wanted to bowl the ball and how I wanted to get those guys out and I just wasn't doing that," Johnson said.

"Hopefully I have passed all that and I can mentally be stronger. I block things out pretty well normally but I think it was just the Ashes, the whole hype of it, and the personal things that came out," the ICC Player of the Year added.