The husband of murdered MP Jo Cox, Brendan Cox, has quit two charities he set up in her memory after allegations of sexual assault were made public.
Mr Cox denied assaulting a woman in her 30s at Harvard University in 2015 - but admitted to "inappropriate" behaviour while working for Save the Children.
He has left posts at More in Common and the Jo Cox Foundation a week after the Mail on Sunday published the claims.
Mr Cox apologised for the "hurt and offence" caused by his past behaviour.
In a statement issued on Saturday, he said: "While I do not accept the allegations contained in the 2015 complaint to the police in Cambridge, Massachusetts, I do acknowledge and understand that during my time at Save the Children I made mistakes."
Save the Children have said the complaints against Mr Cox were investigated in accordance with its procedures.
The charity confirmed that Brendan Cox was suspended and a disciplinary process begun but that he resigned before it was completed.
The charity also announced that its chief executive Kevin Watkins has ordered a review to establish "whether the system for dealing with complaints about behaviour in the workplace can be further improved".
Jo Cox's sister Kim Leadbeater said the family would "support Brendan as he endeavours to do the right thing by admitting mistakes he may have made in the past".
She added that "Brendan is a wonderful father and I have no doubt about the happiness he brought to Jo."
Mr Cox, who married Jo Cox in 2009, was reported to police in Massachusetts in the US in 2015 for "inappropriate touching" while on a trip to Harvard - a claim which he denies.
The father-of-two said some of the allegations against him were a "massive exaggeration", but conceded that he had at times "overstepped the line".
In 2015 the Mail on Sunday reported that Brendan Cox had stepped down from his position as chief strategist at Save the Children over allegations of "inappropriate behaviour" which he at the time denied.
More details of Mr Cox's alleged behaviour emerged after Oxfam issued its own apology over a sex scandal involving aid workers in Haiti.
'Dedication' to charity
Labour MP Mrs Cox was fatally shot and stabbed outside her constituency office in West Yorkshire by a far-right extremist during the EU Referendum campaign in 2016.
Mr Cox said it had become "much more difficult" to focus on the two charities he set up after his wife's death, the community group More in Common and the Jo Cox Foundation.
"For that reason, while away over half term, I decided to step down from my current public roles for the time being," he said.
He added: "In the past I have focused on disputing what I felt was untrue in the allegations, but I realise now that it's more important to take full responsibility for what I have done."
A spokesperson for the Jo Cox Foundation said the charity "admired" Mr Cox's contribution as a trustee.
"The trustees and staff have admired the integrity, commitment and dedication that Brendan has shown in our work to create a positive legacy for Jo," they said.
Speaking on the Peston on Sunday programme Labour MP and friend of Mr Cox, Jess Phillips, said he was right to step down from his positions at the charities.
She said that men were "going to have to address their behaviour" but added she didn't like the idea that "we switch off our feelings about people."
"I love Brendan. He is my friend. His family are friends with my family.
"It's not enough to just say you're sorry, you have to show the way you are going to change in the future.
"And I think Brendan, more so than many I've seen in this area, is actually trying to do that."