Mr Donald said he had not come to the decision easily and it was with "a great deal of sadness and trepidation" that the announcement was made yesterday.
"It was hard to tell the boys. In fact, the boys have become so much a part of my life that I wimped out of telling them," he said.
So, head boy Kai Daniel made the announcement for him by reading his letter of resignation at a special school assembly yesterday.
Mr Donald said he became principal of Kings High School in August 2001, with a commitment to spend up to seven years "doing my very best" for the school's community of pupils, staff and families.
"I have thrived on the challenges, the successes and the real sense of community that Kings has provided over this time.
"I can only hope that I can leave behind a school that has enhanced its reputation as a quality environment to educate our young men within. I will never leave behind the leadership lessons that I have experienced or the memories of a great school that I am so proud to be part of."
Mr Donald said he would finish in late July and planned to begin his duties implementing initiatives at a secondary school in Bani Yas, near Abu Dhabi.
"The school is doing an improvement programme using parts of the New Zealand education model"
Mr Donald was approached about the job on Thursday by an Auckland consultancy firm, because of his experience in the education system.
He was given little time to make a decision but accepted because he believed it was the right time for him and the school.
"This fulfils a dream that my wife, Justine, and I have had to spend time working offshore after kids and before grandkids - not something that is easy to organise."
Mr Donald said he would not miss the paperwork which came with the higher level of compliance in New Zealand schools in recent years.
However, he would miss the "little things".
"I don't think I'll be making any early morning calls to say the school is closed for snow in Abu Dhabi. I'll miss that."
The Kings High School board of trustees will meet next Thursday to discuss the process for recruiting a new principal.
