My coworkers threw me a 20th anniversary party at work last week. I had no idea it was going to happen.
Last week at work, my coworkers threw me a 20th anniversary party at our company office.
user
Oh Wow! 20 years at your job! You must be well liked there. 
assistant
I like to think I am. I had no idea this was going to happen.
user
It must have been a wonderful surprise for you.
assistant