Regnier will work with White (pictured) until the end of the year to ensure a smooth transition and both appointments are subject to regulatory approval.
White has been executive director and chief operating officer at YBS for nearly six years and was previously board chairman for YBS subsidiary Accord Mortgages.
He has also worked as the group chief operating officer at AIB for nearly two years, and prior to that was employed at National Australia Bank for around eight years, most recently as executive general manager for customer processing and payments.
Regnier has been with YBS since 2014, initially joining as chief commercial officer and has been chief executive for nearly five years.
He worked for the Building Societies Association for around five years and has also held senior roles at Money and Pensions and Service and TSB Bank.
John Heaps, YBS chairman, said: “I would like to thank Mike for his outstanding contribution to the Society over the last seven years. He has led the Society superbly through a period of significant challenge as we have addressed both the transformation to a more digitised world and the complexities of the Covid pandemic.
“Our performance this year, including the results at the half year showing strong growth in both mortgages and savings, strong profitability and over £40m of additional value passed back to our members, is a proper reflection of how well the executive has performed under Mike’s leadership.”
He added: “I am pleased that Stephen White, who is currently our chief operating officer, will take over as interim CEO. Stephen has more than 25 years of experience in financial services across the UK, Ireland and Australia, and has been with the Society almost six years. Stephen will ensure we continue to help real life happen for our members and build on the Society’s success of over 155 years.”
He said that it was currently working with executive search partners to find a permanent successor and he expected there to be a number of strong candidates.
White said that he looked forward to “working with my very talented colleagues to maintain momentum, and to continue to deliver our purpose of providing real help with real life”.
Regnier added that it had been a “great privilege” to have been YBS chief executive and said: “I feel that now is the right time for me to take on a different challenge and leave the Society in excellent shape for my successor to take the society on the next phase of its journey.”
Regnier is set to take over as Santander UK chief executive from Nathan Bostock, who has been in the role since 2014.
Bostock joined from Royal Bank of Scotland, where he worked from 2009 as executive director, group finance director and group chief risk officer.
Regnier said that he was honoured to be joining Santander, which he said had a “rich heritage in the UK, a strong track record of innovation and a commitment to helping our country prosper”.
He added: “I am excited to be able to make a real difference to people and businesses across the UK, helping them to thrive and grow with the support of Santander’s incredible team and unique services and products.”