The chairman and chief executive of global public relations and advisory firm Teneo has resigned after reports of drunken misconduct at a star-studded fundraising concert promoted by the Duke and Duchess of Sussex to raise money to supply coronavirus vaccines to developing countries. Declan Kelly resigned from his Teneo positions “effective immediately” on Tuesday, days after he was accused of touching a number of women and men inappropriately and without their consent at the concert, which featured appearances by the Foo Fighters, Selena Gomez and Jennifer Lopez. Kelly, an Irish former journalist turned public relations guru, said in a statement: “I made an inadvertent, public and embarrassing mistake for which I took full responsibility and apologised to those directly affected, as well as [to] my colleagues and clients.” He claimed to have become victim of a smear campaign against Teneo, which bills itself as an adviser to chief executives and senior directors at many of the world’s leading companies, including a “significant number” of FTSE 100 and Fortune 500 companies. “A campaign against the reputation of our firm has followed and may even continue in the coming days. However, regardless of the veracity of any such matters I do not want them to be an ongoing distraction to the running of our company,” he said. After the allegations, first reported by the Financial Times, Kelly was removed from the board of Global Citizen, the charity that hosted the Vax Live coronavirus vaccine fundraising party at which the alleged misconduct took place. Global Citizen is chaired by Prince Harry and Meghan. The fundraiser was backed by Pope Francis and the US president, Joe Biden, who released messages of support at the event. Teneo, which employs 1,250 staff working from 33 offices around the world and a roster of senior advisers including former British ministers Amber Rudd and William Hague, had started to lose high-profile clients as a result of the allegations. Car giant General Motors pulled out of a $250,000-a-month contract with Teneo on Monday. Kelly, who worked directly with GM’s CEO, Mary Barra, focused on government relations and executive positioning, according to the Detroit Free Press. He has also served as an adviser to the heads of Coca-Cola, Dow, IBM and UBS. Kelly’s official profile – removed from Teneo’s website on Tuesday – described him as a “trusted adviser to many of the world’s leading CEOs and corporations”. Kelly was an adviser to Hillary Clinton on her first attempt at running to become US president, and she later appointed him US economic envoy to Northern Ireland. He is a brother of the Irish Labour party leader, Alan Kelly. Teneo, which Kelly co-founded in 2011, said he would be replaced immediately by his fellow co-founder and chief operating officer, Paul Keary. The third co-founder, Doug Band, left the firm – which was valued at $700m following an investment from venture capital group CVC – earlier this year. “We want to thank Declan for his leadership and dedication over the past ten years in building Teneo into the world’s pre-eminent CEO advisory firm,” Teneo said in a statement.