To cap/top it all
Definition 1 of 1
Pro Tip 1/3Negative Climax
Use 'to cap/top it all' when the final event makes a bad situation worse. 
The day was awful, and to cap it all, I missed the last train home.
Pro Tip 2/3Conversational Tone
This phrase is informal, suitable for conversations rather than formal writing. 
I lost my keys and to top it all, my phone's battery died.
Pro Tip 3/3Unexpected Twist
It emphasizes an unexpected event that completes a bad experience. 
After a week of problems, and to cap it all, I now have to move out.