James DeGale retires: Former Olympic & world champion quits at 33
James DeGale, the first British boxer to win an Olympic gold medal then a professional world title, has retired.
The 33-year-old lost on a unanimous points decision to Chris Eubank Jr in London on Saturday.
"It's been an unbelievable journey," said DeGale, who won 25 and lost three of his 29 fights as a professional.
"It's hard to admit that I'm not the fighter I once was. I'm human and, along the way, my injuries have taken a toll - both on mind and body."
DeGale beat American Andre Dirrell on points to claim the vacant IBF super-middleweight belt in May 2015.
He lost his title in December 2017 but won it back in an April 2018 rematch with American Caleb Truax.
However, he gave up the belt in July 2018 to focus on chasing "massive fights" rather than facing mandatory defences.
Before the fight with Eubank Jr at the O2 Arena, DeGale said he would "knock it on the head" if he lost.
"Today marks 10 years since my professional debut fight on 28 February 2009," said DeGale.
"It's been an unbelievable journey and I've had an amazing decade - if I'm honest, the best years of my life - and, having started boxing at the age of nine then being selected as part of the England amateurs squad, I've collected many memories along the way."
'You've made the right decision' - Groves' message to DeGale
George Groves inflicted the first defeat of DeGale's professional career to narrowly win the British super-middleweight title on points in 2011.
"I've given him a lot of stick the past week after his loss at the weekend, but upon his decision to retire today I want to wish James DeGale well in the next chapter of his life," said Groves, who retired in January.
"You've made the right decision. It's a tough sport and you reached the highest level. Congratulations."
'He left an indelible mark' - analysis
BBC Radio 5 live boxing's Mike Costello and Steve Bunce
Costello: It was a brilliant win in the United States by James DeGale to win his world title, which very few British fighters have done in winning a world title.
He has left an indelible mark on the sport - there is no doubt about that - as an amateur and professional.
Bunce: The line he kept using was 'I'm a history man' and he's absolutely right.
It's not just the winning of world titles, regaining a world title, losing world titles in hard, scrappy fights and that early defeat by George Groves early in their careers.
I also like that relationship with his trainer Jim McDonnell. If we're in this seat in 10 or 20 years then we will not be talking about a guy who has been with a someone for 10 years and who has lost a couple along the way.
What we are seeing is the passing of a relationship, also a passing of a bit of old-school boxing history - a seasoned coach being with a young kid all the way through to the end. That might be the last one.