How about this?
TO WHOM IT MAY CONCERN
This is to certify that Mr [insert full name] has been employed as a [state job] with the Agency since [date commenced.] Recently, however, he felt it his duty to relinquish his post in order to spend quality time with his wife - who resides in the Philippines - with a view to her ultimately applying for a Spousal Visa/EEA Permit to come to the UK.
Due to the circumstances, I reluctantly agreed to accept his resignation - since it is his intention to visit her homeland for a period of at least 3 months ... and he, himself, considered it would be unfair to expect the firm to hold his job open throughout his prolonged absence.
Might I just add that, although I was saddened to lose the services of such a diligent and respected member of staff as Mr X, I fully understand his decision. I wish he and his wife every success for their future together, and have no hesitation whatsoever in recommending him to any subsequent employer on his return.
Yours faithfully,
*Goodluck to both of you!
