Amy Turner, who was set to be part of England's World Cup coaching staff, has joined Harlequins Women as head coach.
Former England forward Turner, who also coached the national under-20s side, previously played for Quins before becoming assistant coach at the club.
Turner told BBC Sport she "just couldn't turn down" the opportunity.
Her appointment leaves England without a female member of coaching staff for the World Cup in New Zealand, which is being held in October and November.
The Rugby Football Union (RFU) said it was "working in collaboration with World Rugby on next steps" to find a replacement. England's first match in the tournament is against Fiji on 8 October.
Following the departure of Gerard Mullen, who led Quins to the Premier 15s title in 2021, Turner will be supported by assistant coaches Brent Janse van Rensberg, formerly defence coach at Bath's men's side, and Harlequins full-back Ross Chisolm.
Matt Walson joins from Melbourne Rebels as a strength and conditioning coach.
Quins director of rugby performance Billy Millard said: "Amy is a talented coach who knows the Premier 15s and the women's rugby landscape extremely well.
"We are dedicated to support her development into the best female coach in England and we are excited to have her lead our programme into its new era."
Turner said she was looking forward to the new coaching group "putting our heads together" and "getting the players excited about intense, hard-felt, passionate, Harlequins-style rugby".
England left with hole to fill
Turner was set to join England in New Zealand as part of World Rugby's coaching intern programme, which is designed to make sure every team has a female coach at the World Cup and achieve 40% female representation in international coaching by 2025.
The former police officer's departure leaves the Red Roses - who go to New Zealand as world number ones and favourites to win the title - with a vacancy to fill at short notice. There are many women in the England backroom team, but Turner was the only female coach.
Turner believes her new role proves the internship worked, saying: "It's designed to put women in places to get roles in high-performance environments.
"It wasn't a hard choice. I've been involved as coaching staff for the last two of England's autumn international campaigns, seen them evolve into a really professional, physical outfit."
Turner added England head coach Simon Middleton was "really, really happy for me".
The RFU is advertising for a new Under-20s coach.
'I'll bring players in if needed'
Most Premier 15s sides have already completed their player transfers for next season, with Gloucester-Hartpury making some of the most eye-catching signings, including the acquisition of young England prop Maud Muir from Wasps.
Quins are yet to make any such high-profile signings but Turner said: "If I felt there is a need to bring any more players in, I'll be having discussions to make plans to do that.
"If there was a need to strengthen our depth in areas, Harlequins have made it known they are investing in the women's game."