(Tom de Castella is a London-based freelance writer whose work appears in the Financial Times and BBC Online.)

KP is kaput. The surprise is it's taken so long. After his famous Ashes-winning 158 not out at the Oval in 2005, some Englishmen may say it's been worth it whatever else happens. But with only two months before the team arrives in Australia, Kevin Pietersen is all washed up. His self-pitying tweet after being dropped from England's one-day squad against Pakistan summed up not only his fall from grace but his bewilderment at the world he finds himself in. "Yep...Done for rest of summer!!Man of the World Cup T20 and dropped from the T20 side too..It's a fuck up!!"

It's dangerous to start talking about things being inevitable. Wasn't Federer supposed to be finished a couple of years ago and Nadal irrevocably crocked just a few months ago? But having made that qualification, the demise of Pietersen always seemed likely. There was something slightly odd about the way he turned up in the England side after alienating first his native South Africa then his first county, Nottinghamshire. (He recently fell out with Hampshire and is now on loan at Surrey, where last week he was pictured fielding, above.) On the strength of an English mother, heaps of runs and a tattoo of the three lions, the Barmy Army quickly accepted him. The Pietermaritzburg twang was a minor embarrassment. But few here remembered that when we won the Ashes at the end of his first Test series.

The crazy decision to make him England captain in the summer of 2008 and his sacking after just three Test matches sowed the seeds for this summer's meltdown. Two months after his forced resignation, following a poor series defeat in the West Indies, Pietersen admitted he was still brooding at his treatment. Now 18 months on he's still brooding but the glumness seems to have morphed into a fullblown identity crisis. Apart from an 80 at Edgbaston, he managed scores of 9, 22, 6, 23 and 0 in this series with Pakistan. Before the final Test he confessed: "I'm nowhere near the person I used to be, but I've got to keep trying to work at it. I'm trying so hard every day to get back to where I used to be." It sounded like the despairing words of a celebrity wifebeater rather than the man who is second only to Don Bradman for the number of runs scored in his first 25 Tests.

Theories for his demise have been various and unconvincing. Writing in the Daily Telegraph Simon Hughes, said that KP was suffering from a "sophomore slump" and struggling to regain his appetite: "Pietersen is clearly a man adrift. He needs our sympathy not our scorn." Meanwhile Simon Barnes in The Times compared him to the apotheosis of enigmatic genius, former France and Manchester United footballer Eric Cantona. "Now, to his horror and disbelief, he is faced by the radical possibility that he is not a great cricketer after all. Just a very good one." He needs to choose between settling for the latter or being a genius, Barnes wrote, although unhelpfully neglected to say how he might achieve greatness again. Ricky Ponting, who enjoys debating English flaws at any time of year but especially in the months leading up to the Ashes, might advance a different argument: that the inherent mental weakness of the Poms has finally poisoned even Pietersen's seemingly endless reserves of self confidence.

There's certainly poetic justice to his demise. We wanted him for the obnoxious self confidence that made him fall out with everyone in his native land, for his peacock-like qualities that resulted in Dead Skunk and blue-dyed barnets and outlandish, devastating shots. The selectors took a gamble and came up trumps bringing the world's most successfully aggressive batsman into the England team. But then that self confidence led to hubris - exhibit A being his crass attempt as captain to get the coach Peter Moores sacked.

That incident highlights the egomaniac who's never fitted into a team. It was on view again last month when he tweeted about Graeme Swann's drink driving court case. Swann had claimed that he'd dashed out in his Porsche Cayenne in the small hours of the morning to buy a screwdriver so that he could rescue his pet cat who was stuck under the floorboards. This was Pietersen's helpful comment: "2 hours with @Swannyg66 this am and I'm still not having this 'cat' story!! Haha." Swann, whose case has been adjourned until 7 October, didn't appear to appreciate having his legal defence publicly rubbished by someone in his own dressing room: "Such a shame my teammates are so remedial in their 'banter'. Must be because they're all south African."

The media is often writing off the greats years before their sell-by dates. And right on cue Pietersen scored a century for Surrey at the weekend - his first ton for 18 months. But it was an unimportant match, that peacock swagger has gone and who knows how long the psychological scars that would have disappeared in an afternoon on the Playstation, will haunt him for now he's 30. In the memorable words of the Guardian's Barney Ronay, Pietersen "functions best while in possession of a head that is almost entirely empty." Whereas now in midlife crisis mode he is "like the kind of male friend who will hug you for slightly too long and maybe even nuzzle your neck despite the fact neither of you are drunk, it's 11.30 in the morning and you only came by to borrow a squash racket."

Forget genius then. From this vantage point, Pietersen as a "very good cricketer" would be welcome news for England. But deep down one wonders if his South African otherness - so useful when he first arrived - now marks him out as a brooding, lonely soul with no way back. How he responds in the snipers' alley of Ricky Ponting's close field setting will be one of the most intriguing stories of the Australian summer.