I'd love to, but I'm afraid I have a previous engagement.

我很宁愿答应往，但生怕已跟他人事前有约。

youdao

I can't see you on Monday because I have a previous engagement.

星期一我不能见你，因为我有约在先。

youdao

I cannot see you on Monday because I have a previous engagement.

星期一我不能和你见面，因为我有约在先了。

youdao