Leaked iMessage

I bought an iPhone recently (couple months ago) and my current number I’m using on the phone is from my plan I started with T-Mobiles couple months ago. The misery that remains unraveled for me now is:

A friend sent me a message (iMessage) and all of a sudden, conversation from 2 years ago appeared in our chat and this conversation contains some private picture of myself. What’s even more confusing is that I never had this phone or this number at the time of my this said conversation.

How possible is this?