Wow, that was a shock !!!
Here's the announcement cut-and-pasted from itv-f1.com ....
Jenson Button will make a sensational return to Williams next year, according to reports.
Button rejoins the team he made his F1 debut with in 2000. He will partner Mark Webber in an all-new driver line-up.
The Brit said: "I am very pleased that I had the option to re-join the BMW Williams team where my Formula 1 career started.
"For the meantime the 2004 season has my full focus and attention.
"Beyond this, I have every confidence that the massive investment in resources and the depth of talent at Williams and BMW provides the best platform for my future ambitions to be a world champion."
Frank Williams made his move after Button's current team BAR allowed their contractual option on his services to lapse.
Williams told BBC Radio Five Live: "He has been under option to his present team BAR for some time.
"The option expired recently and Button's management called us to say that the option was no longer valid and would we be interested in his services - and of course I reacted as you might expect me to.
"I think they (BAR) probably wanted to take up the option but whether they've executed or not will come out in due course."
Button has signed a two year contract with the team. Asked if he thought the Brit could win the world championship in that time, Williams said: "If we give him a good enough car, most certainly yes.
"He's on a strong upward path, every drive he improves."
The move comes as a massive shock because Button and BAR have made huge strides this season. The 24-year-old's name had not even been mentioned in rumours over Williams' 2005 driver line-up.
BAR are also 29 points ahead of Williams in the constructors' championship.
Asked why he thought Button had made the decision to return, Williams said: "He started with us in 2000 and we've been in very close contact all of the time since.
"Maybe he just harboured a wish (to return) and recognised we had spent tens of millions of pounds reinvesting in the company technically speaking.
"Maybe he recognises we have a greater opportunity of providing him a world championship car than his present team.
"I haven't asked him the real answer yet."
Ironically, the move could prevent Button from becoming a grand prix winner this season. Departing drivers are usually frozen out of teams' development programmes, meaning colleague Takuma Sato is likely to have first call on any new innovations.
So what might this mean for Coulthard ? BAR????