I apologize for the delay in the reply.
I apologize for the late reply.
I am sorry for the delay in my reply.
I apologize for the delay in my reply.
I apologize for the late answer.
I'm very sorry for the late reply.
I am sorry for the delay in my reply.
I apologize for the late reply.
I apologize for not replying right away.
I am terribly sorry that my reply is late.
I am terribly sorry that I was late to reply to you.
I'm terribly sorry about my late response.
I am sorry for my late reply.
I apologize for the late reply.
I'm sorry for my late response.
I am sorry for the delay in my reply.