Trudie Davies, chief executive at Gateshead Health NHS Foundation Trust, will serve as acting chief executive at NCIC from 28 July.
Simpson said: ‘I've been asked to support the Humber Health Partnership on a temporary basis and am pleased to contribute to the wider NHS during this time.
‘I know NCIC will be in safe hands with Trudie, who brings a strong track record of leadership and is already well known to many colleagues through our work in the Great North Healthcare Alliance.'
The arrangement reflects the growing collaboration between NHS trusts across the region to support stability, resilience and shared leadership.
NCIC chair, Steven Morgan, said: ‘Lyn has led NCIC through some of its most significant challenges and improvements. We fully support her temporary move to support our colleagues at Humber and warmly welcome Trudie to the trust from 28 July.'