Williams saw red for the shoulder charge on Watson in the first half of yesterday’s dramatic match and left his team-mates to battle on for 56 minutes with 14 men.
Williams will now sit out the final and deciding Test in Aukland next weekend and miss another three weeks on top.
“Just finished my hearing, ended up getting four weeks,” Williams told reporters outside New Zealand Rugby headquarters in Wellington on Sunday.
“Obviously really disappointed, but happy with being able to get in there and say my piece.
“They’ve come to the conclusion that it was reckless, it wasn’t intentional.
“I’ve got in contact with Anthony and I’ve apologised to him, but very disappointed that I was sent from the field last night and let my brothers down.”
All Blacks coach Steve Hansen had earlier called Malakai Fekitoa into the squad in anticipation of Williams receiving a ban and explained how upset the centre had been to receive the red card.
“He’s disappointed, not for himself, he accepts that he’s made a mistake,” Hansen said.
“He’s disappointed because he’s let the team down.
“One of the biggest mantras in our team is that the team comes first and he knows he let the team down.
“But we can’t go back and change it either. People make mistakes. It’s a fluid game, it’s a fast game and unfortunately he’s made a mistake so we have to move on from it.”
Williams was just the third All Blacks player to be sent off in a test match, with Cyril Brownlie the first against England in 1925.
Colin Meads was also sent off in 1967 against Scotland at Murrayfield in Edinburgh.
After the match – which the Lions sealed a stunning comeback in late on thanks to a try from Conor Murray and the conversion from Owen Farrell – All Blacks coach Steve Hansen refused to blame the red for defeat.
He was gracious in defeat and admitted the Lions deserved to level the series.
“The red card was a red card, if the ref says it’s a red card, you don’t have any say in it,” Hansen said.
“It was one of those ones that could have been a yellow or a red, but he chose it to be a red so you just have to live with it.
“There’s no point whining about it, Sonny didn’t use his arms so he put himself at risk, and unfortunately he collected young Anthony’s head and put him at risk.
“You don’t want that and the referee deemed it a red card, so off you go boy.”
