Paul Gustard insists he is leaving the England coaching staff with the RFU's blessing, and believes Eddie Jones will see his departure as a "good challenge".
The-42-year-old is leaving his role as defence coach with England to take up a new position as head of rugby at Harlequins, although he will still take part in the tour of South Africa.
It leaves Jones without one of the key members of his coaching staff just over a year before the World Cup, but Gustard says the head coach will see the positives in the situation.
"Eddie Jones quite likes change and he quite likes fluidity and I'm sure if you ask him, he will look at this as a good challenge for the team and the rest of the coaching team", said Gustard.
"I've really enjoyed my time there and the success we've had - some unbelievable memories. But some of the skills I've picked up, I'm now really looking forward to taking into this role here at Harlequins.
"I'd rather make a decision and regret it than sit back and regret not doing something. I've not walked away lightly, but I've walked away to something I'm really excited about.
"It gives me a great opportunity to progress my career and I go with the full blessing of the Union."
Gustard joins a side that finished tenth in the Aviva Premiership this season, but he believes Harlequins have far more ability than their lowly league finish suggests.
He said: "It's a club that hasn't performed as well as they can do. They've got more talent than their league position demonstrates.
"They didn't defend as well as they could do - that's obviously an easy area for people to align me too.
"I think we need to pick up some work around the line-out as well. They're two key areas we will be focusing hard on."
The RFU has confirmed the recruitment process for a new defence coach is already underway, and Jones provided a glowing reference for Gustard.
The Australian said: "I wish Gussy all the best at Quins. He is a talented young English coach and a very good choice for the role.
"He has made a big contribution to the England coaching team as our defence coach and I'm happy that he has this opportunity to develop and prove himself in a head of rugby role."