Dear
Your letter arrived a few days ago and I must confess that this obligation completely slipped my mind. Needless to say， there is no excuse for this and I extend my sincerest apologies along with the attached check.
Please accept our warmest regards and sincerest hope that all is well. We certainly look forward to meeting you in the near future.
Again， thank you for the hospitality you extended to our son during the vacation period. I am sure Rob has enjoyed and will continue to enjoy the friendship of your son.