Peterborough said the decision to sack Williams had not been “taken lightly” but added that the board “felt it had no other choice but to make a change”.
“The team’s form in League One has not matched the board’s expectations, particularly given the significant investment made in the squad,” the club said in a statement.
Peterborough’s summer recruitment drive included bringing Danny Ormerod from AFC Fylde in for a fee of at least £600,000, while Ethan Williams was said to have cost a “sizeable” sum when he was signed from Manchester United.
Williams, who took time out from football after losing his job at Swansea to work as a customer care assistant at Bristol Airport, won 18 matches and lost 20 in the 47 he took charge of.
His time at Weston Homes Stadium has been the shortest of his managerial career which started with a spell at Swindon Town that came to an end in May 2017.
He went on to work as an assistant manager to Russell Martin at MK Dons and Swansea before he got another shot at being the boss with Notts County – a club he guided to promotion from the National League in 2023 before moving on to take the helm of Swansea in the Championship in January 2024.
Williams’ replacement has not been immediately lined up at Peterborough, who have put the existing coach team of assistant manager Ryan Harley and coach Connell Rawlinson in temporary charge.