A student at Florida's Stetson University has graded an apology letter sent to him by his ex-girlfriend and sent it back to her with a mark.

Instead of throwing it away, Nick Lutz decided to get a red marker out and critique the four-page note.

He gave his ex 61 out of 100 and a D- for her effort.

"Long intro, short conclusion, strong hypothesis but nothing to back it up. Details are important," he wrote on the final page.

He starts off his letter by saying the introduction is too long and there's lots of repetition.

Nick says his ex needs to show reasoning when saying she ended up failing to keep the relationship working.

He also says she needs to back her claims up with proof, like saying she never cheated on him.

The second page calls for his ex-girlfriend to provide more details after this line: "I took all the promises we had and broke them."

Then there's a spelling mistake with "loose" changed to "lose".

Nick then calls his ex out when she says she has "no reason to hide, lie or hold anything back" from him.

He writes in the margin: "If there is no reason to lie, why isn't the truth being told?"

He says he hasn't thought about her when she asks if he has and again accuses her of "using useless fillers" to pad out her letter.

Nick even says she used "lackadaisical" handwriting near the end of her note.

The final page contains a question mark after "I love you" and also the rest of Nick's final conclusion.

"If you want to be believed, back it up with proof," he writes.

"You claimed that cheating never occurred, but place blame on yourself - then what for?

"Need to stop contradicting your own story and pick a side. While this gesture is appreciated, I would prefer details over statements.

"Revision for half credit will be accepted."

Other people pointed out other mistakes in the letter.

Nick also told another Twitter user that his ex-girlfriend had seen the changes and was "okay with her grade".