Shawn Porter confirmed that he would retire from boxing in the wake of his defeat to Terence Crawford and his father’s admission that he "didn’t prepare like I wanted".
Porter was stopped for the first time in his career when Crawford floored him twice in the 10th round to successfully defend his WBO welterweight championship.
He later revealed that, regardless of the result, he had planned to end a boxing career that yielded two reigns as world welterweight champion.
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Kenny Porter, his father and trainer, explained why he pulled his son out after the second knock-down: "Honestly? He didn't prepare like I wanted him to prepare so I didn't want him in that situation.
"When guys get to certain levels they think they know what they are doing, and they don't take on information.
"It was an easy decision for me.
"My kid was at a deficit, he couldn't defend himself, I had to protect him."
Porter later said: "I understand my dad. I took too many clean shots which isn't the Porter way."
He confirmed his retirement, admitting he only remained in the sport after fighting Errol Spence Jr in 2019 to earn a crack at Crawford.
He looked at his father and said: "This is a conversation we have not had."
But Porter's father responded: "I already knew this.
"He thought Errol Spence Jr would be his last fight. I'm his father, I knew that!
"I know things before they happen. This was something that was coming.
"I could see it in training, in his movement, how he looked at the clock like 'how long do I have to be here for?'"
Porter won 31 of his 36 fights and owned the IBF and WBC titles.
He has boxed the division's elite - Crawford, Spence Jr, Keith Thurman, Danny Garcia, Yordenis Ugas, Paulie Malignaggi and Adrien Broner.
His first loss was inflicted by Britain's Kell Brook in 2014, when the Sheffield fighter first became a world champion.
Porter said about hanging up his gloves: "I won't become a gatekeeper. That's not the life I want to live.
"I'm 34 - now's the time."
Sky Sports Boxing schedule
December 11 - BOXXER in Cardiff
Chris Eubank Jr vs Liam Williams
Claressa Shields vs Ema Kozin
December 11 - Top Rank in New York
Vasiliy Lomachenko vs Richard Commey
Jared Anderson vs Oleksandr Teslenko
Nico Ali Walsh
December 17 - Top Rank in Montreal
Artur Beterbiev vs Marcus Browne - IBF and WBC light-heavyweight titles
February 26 - Top Rank in Glasgow
Josh Taylor vs Jack Catterall - undisputed super-lightweight title