Williams will draw the curtain on his illustrious career when he runs out for the Barbarians against Wales on Saturday, but he is already delighted with the end of his 15-year professional career.
"I enjoy success of like anybody else. The one you remember is the latest one and this for me is a great way for me to finish," admitted the 35-year-old wing.
"I am very proud of the fact that I am associated with the Ospreys. We have worked very hard this season, we have had our ups and downs and there has been a lot of change in the ranks, with a lot of players leaving the region.
"For us to stick at it the way we have this season it's a compliment to the guys. I will never forget this day.
"It's up there with anything I've achieved in my career. To go out with a couple of tries in a final in your last game for the region means a huge amount."
Williams will line-up in a star-studded Barbarians side, which is also likely to include South Africa World Cup winning captain John Smit, former Cardiff Blues centre Casey Laulala and fellow All Black Mils Muliaina.
The match will be Rob Howley's first in charge, as Warren Gatland continues to recover from two broken heels.
Howley and the Wales squad that faced the Baa-Baas will then jet to Australia to join Shaun Edwards and an advanced party of players in preparation for their three-Test series with the Wallabies.