Double-act of Grimsey and Hoskins comes to an end nearly a year after they were brought together for retailer's turnaround.
Bill Hoskins has left Focus DIY citing family reasons for his departure.
The finance director said that after signalling his desire to leave at the end of December last year, he now wished to spend more time with his family.
A replacement has been sought in the five-month interim – Andrew Unitt, former finance director of Experian, Boots Healthcare and Halfords.
Mr Hoskins came on-board in June 2007 with Bill Grimsey to revive the fortunes of Focus.
The 'Two Bills' – as they became known – were installed at Focus DIY after the sale of the retailer to US hedge fund, Cerberus.
The pair turned around Wickes before it was sold to Focus Do-It-All for £289m in 2000.
Focus said in a statement: "After a very busy period of being involved in the restructuring of the business, Bill Hoskins has made the difficult decision to resign his position.
"The nature of the business has meant a considerable amount of time away from home and this will now allow him to spend more time with his family."
During his spell at Focus, Mr Grimsey oversaw a sale of 40 stores last year, and a recruitment drive to strengthen the management team.