The gifted Ospreys wing, Wales' record international try-scorer, will make his World Cup farewell in Friday's bronze medal match against Australia at Eden Park.
The 34-year-old has amassed 56 Wales tries, putting him second behind Australian legend David Campese's world record mark of 64.
But after winning 85 caps, it looks as though the finishing line is in sight for one of Wales' greatest players.
"It is an emotional time," said Williams, ahead of facing the Wallabies.
"I keep saying I would like to play forever, but that's not the case. And emotion aside, it's a big game anyway. We are a proud bunch of guys and we want to go out of this World Cup in style.
"This is my last tournament, and what a way to go out. We would have loved to have got to the final, and we did everything in our power to get there.
"The effort from start to finish has been incredible, and it has been a great campaign to be involved in.
"It would be fantastic to bow out at the Millennium Stadium, but I've got to get this game over with first, so let's wait and see.
"It is a time I have been dreading for so long, but I have had a great time. I have had my ups and my downs, but I wouldn't change a minute of it to be honest."
Williams made his Wales debut against their semi-final conquerors France in 2000, but he admits he has rarely enjoyed his rugby more than during the past few months.
"I think the group of boys I have been out with in this campaign, the belief and the work-rate, have been amazing," he added.
"Off the field and on the field it's been incredible, and it has been one of the most committed squads I've been involved in.
"I've always said I would rather retire than be retired, and nothing has changed there. You know when it's time to move on and let the young pups through - and there are a few of them, unfortunately!
"They are not far off pushing me out of the squad. I know that, and everyone else knows it.
"But like I said, I've had a great time, I've loved every minute of it, especially this tournament. Even though a place in the final wasn't to be, it has been a great couple of months and it is time to move on.
"I don't know what I am going to do next. I haven't thought that far ahead, but it will be something to do with rugby.
"I am still contracted with the Ospreys and I will have some rugby to play there. I will be fully committed to that job.
"After that, who knows. Every time I've thought about that it depressed me. It will come to a time where I have to think about it, but not yet."
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