England defence coach Paul Gustard says he shelved contract extension talks with the Rugby Football Union (RFU) to become Harlequins' new head of rugby.
Gustard, 42, will leave Eddie Jones' coaching team after the upcoming tour of South Africa.
Despite the proximity to the Rugby World Cup, the former flanker says he could not turn down the "amazing opportunity" at The Stoop.
"I wasn't coveting this position," he told the Rugby Union Weekly podcast.
"I was all set to help England win the World Cup in 2019. We were in negotiations about extending my contract, but it's an unbelievable opportunity.
"I've got the ambition to be a head coach and I want to make the most of it. Everyone has to step out of the shadows at some stage."
Gustard denies that tensions with Jones were behind his hasty exit from the England set-up, and feels he has improved greatly as a coach under the Australian's guidance.
"He's been brilliant, I have a lot to thank Eddie Jones for," Gustard said.
"He was the first person to give me an opportunity in 2008 as a skills coach, and then gave me an unbelievable privilege in 2016 to represent my country [as a coach].
"He has challenged me and he has made me change as a coach for the better. I've improved immeasurably over the last two-and-a-half years."
And Gustard insists he will be able to balance the twin demands of coaching England against the Springboks, while also planning for Harlequins' pre-season.
"I've got a priority to make sure we win 3-0 in South Africa, that's my commitment to England," he said.
"In my downtime over in South Africa I have to make sure our preparations for pre-season are laid down."