Dear _____（人名）,
It has been a while since we last met. There will be a _____（内容）at/in _____（地点）on _____（时间）. We would be honored to have you there with us.
The occasion will start at _____（具体时间）. This will be followed by a _____（进一步的安排）. At around _____（时间）, _____（另一个安排）.
I am sure the above invitation would have interested you, and just to make sure things will happen as expected please kindly reply to this letter and upon then I will arrange things accordingly. Look forward to seeing you by then.
____My best wishes to you and your family.
______（落款）
亲爱的_____（人名）,
自上次一别已有很久了。

将要有一个_____（内容）在_____（地点）在_____（时间），我们非常荣幸地邀请您来跟我们一起参加。

活动将在_____（具体时间）开始，之后将会_____（进一步的安排）大约在_____（时间），_____（另一个安排）。

相信以上的邀请已经打动了您，为了确保一切按计划进行希望您回复我，我会相应的做好准备。

希望结届时见到您。

祝您阖家欢乐！
______（落款）。