The powerful No.8 was named man-of-the-match in their final pool game - a 56-3 thrashing of French outfit Oyonnax - but that was little consolation.
And his attentions now turn back to the GUINNESS PRO12, starting with Benetton Treviso on Saturday, as Ulster seek to secure their place in the top six and push for a spot in the end-of-season play-offs.
"It was all in vain at the end of the day," Williams told the Belfast Newsletter. "I love playing with this club and it has rekindled my love for the game and I always be forever grateful to them.
"But I'm still here for another three months and I'll be doing the best I can to make it a successful season and hopefully help Ulster qualify for the Champions Cup next season.
"It just seemed to work for me and my family here and unfortunately for reasons out of my control people have to move on.
"We did all we could do on Saturday afternoon and unfortunately results didn't go our way.
"We probably didn't help ourselves earlier in the season but there is always a silver lining and that is we just get to concentrate on the PRO12 and the next six weeks is going to be huge for us."
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