I don't want to believe it either, Simon. He will continue to play for Essex and hopefully there will be one last chance to see him in a Test match, the final Test in England's series with India beginning at The Oval on Friday. Join the team covering that one if you can. Many thanks for all your contributions today and here's to Cookie. Cheerio now.
Simon James George: Noooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo - breath - oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo
BBC Radio 5 live
There will of course be much more reaction to today's announcement in Tuffers and Vaughan from 21:00 BST on BBC Radio 5 live, including an interview with Cook's mentor Graham Gooch.
- Copyright: BBC
Essex team-mate Varun Chopra...
Rob: A hand shaker not a fist bumper. Last of the old school. Thanks for the memories Cook.
Ever gracious, Alastair Cook paid a lovely tribute to his family in his Test retirement statement. His wife Alice is expecting their third child in the near future. "My family and I have had 12 wonderful years fulfilling my dreams and this could not have been done without them.
"So I wish to thank my parents and brothers, my wife, Alice, and her family for their quiet, unwavering support behind the scenes. As cricketers, who travel frequently, we often don’t realise just how important our families are to our success."Copyright: Getty Images
Tim in Marlow: Regarding Cook's average. First, he scored his runs as an opener - which is inevitably more difficult than as a number three or four. And second, the last ten years of his career have featured DRS; we are yet fully to analyse the impact that will have on averages in general.
Former England cricket coach and Sky Sports pundit David Lloyd on Twitter...
Chris in Beckenham: Genuinely gutted Cookie has retired. At the age of 33, he still has so much to offer. Might be going through a bad patch now, but the cream always rises to the top. Thank you for everything you have done for your country. An absolute legend.
Then there is his alter-ego on the family farm near Leighton Buzzard in Bedfordshire and he told the BBC's Countryfile programme in 2016 of his combined love for cricket and farming: "They are both my passions and not many people can say what they do for their job or their life is what they love doing all the time."
It was with this in mind that he made a very special journey on his wedding day on New Year's Eve in 2011. Much better than a groundsman's roller.Copyright: Getty Images
Cook has achieved plenty on the cricket field but here's our chance to show a couple of pictures of him that you may not have seen.
Another of his many records must surely to be the first person to play international cricket and sing publicly with Dame Kiri Te Kanawa. Here they are at St Paul's Cathedral, about to belt out the tunes for Her Majesty The Queen.Copyright: St Paul's
Thomas Lawler: I was in Afghanistan for the Ashes 2010/11. The cricket was on the TV above the Ops Room map table permanently. Cook’s 235no in the second innings of the first Test will remain with me forever.
Former Pakistan all-rounder Azhar Mahmood...
Margaret in London: Lucky enough to see his first century in Nagpur....hope to see his last at the Oval at the weekend.
Former Australia cricketer Tom Moody...
Jon Precious: Cook had to retire IMO before his status as an absolute legend ran the risk of becoming tarnished. Quite simply, England's greatest batsman surely? Big, big shoes to fill for whoever the selectors choose to replace him for the winter. Those stats!