The Athletic attacker was taking part of an Amazon documentary, 'Six Dreams' which provides behind the scenes access to the 2017/18 campaign.
A scene in the documentary shows Williams speaking to a young black child about his career, and everyone was left stunned by his response.
August 9, 2018
"It is very difficult to get to Athletic, the first team, you are an example for all of Africa and I feel very proud and I congratulate you too," the young man said, addressing the Basque attacker.
Williams replied: "Thank you very much, really, because in the end it makes me proud that all black and African people feel proud of me, I want to open people's minds that a black man can not play in Athletic or 'that black is not Basque', which is still happening today."
"Listen or read comments: 'How can a black man play for Athletic?' No, no, I'm black, but I'm also Basque, I was born here, I feel Basque and I want to open all the doors to people who want to fight and work and work hard to play in Athletic," he concluded.
Williams' speech has done the rounds on social networks, with many people taking heed of his example, and praising his honesty.