He claimed to be an 18-year-old Marine heading off to war, and she alleged to be an attractive young woman sending him off with provocative pictures. Or so they thought. However, they were actually two middle-aged people carrying out a fantasy internet relationship that seemed like a harmless lie.

Sources:

When Catfishing Turns Into a Deadly Love Triangle - Life (livingmgz.com)

Also, the 2009 documentary film Talhotblond.