Lo, who retires in December, has worked with Fleet Mortgages since its launch in 2014.
Prior to that he worked at CHL Mortgages for around 14 years in various roles including finance director, head of finance, treasury and securitisation and chief accountant.
Before that he was group financial controller and finance director at Kestrel Holdings, and was also an auditor at EY, Blick Rothenberg and Credito Italiano International.
Incoming CFO Richardson has been head of finance at Fleet Mortgages for around seven years.
She was previously a treasury accountant at CHL Mortgages for nearly three years, and before that worked at Baker Tilly for five years most recently as an audit supervisor.
The lender has also promoted human resources head Kim Beaven to the role of HR and facilities director and Diane Mitchell will take on the role of credit director. Mitchell was previously head of credit.
Beaven has been with Fleet Mortgages since 2014 and previously worked at CHL Mortgages for around a year. She has also held HR roles at Surry and Sussex Probation Trust, Voyage Care and Solor Care.
Mitchell has worked at Fleet Mortgages since 2014 and before that worked at Capital Home Loans for around 11 years in various roles.
Bob Young, senior executive officer at Fleet Mortgages, said: “Having worked with Sunny for over two decades, it’s somehow hard to believe he will be retiring next month, but he has been a huge part of what we’ve been able to achieve at Fleet, and the entire team here wish him a wonderful and long retirement.”
He praised Richardson, Beaven and Mitchell, adding that to “say they are brilliant at their jobs would be an understatement”.
He added: “We are fortunate to have them and I have no doubt they will continue to be huge assets to the business.”
Fleet Mortgages was acquired by Starling Bank for £50m in July, with all of its mortgages now being funded by Starling’s deposit base.
The firm has recently reached £2bn assets under management for the first time and November was the first full month Fleet originated business for its new funder, with Young adding that it looked like it would be a record month of lending.
He said: “The future therefore looks particularly bright for Fleet and we will have more to say and offer for the rest of the year and into 2022.”