The former Barcelona goalkeeper tragically committed suicide in 2009, having stepped out in front of a train in Neustadt am Rubenberge in Germany.
It was later established that Enke was suffering from severe depression, something he had battled since the death of his young daughter in 2006.
And now, on the eighth anniversary of the 29-year-old’s death, Mertesacker has published a heartbreaking tribute on Enke’s wife Theresa’s blog.
The Arsenal defender reveals how he had just broken into the Hannover first-team when Enke joined the Bundesliga club in 2004, with the pair immediately forging a strong friendship.
Mertesacker wrote, “I was a 19-year-old freshman who had just completed his first Bundesliga games when Robert entered our locker room at Hannover 96 in the summer of 2004 and greeted me: ‘Ah, hello, and you’re the Per.’
“He came from Spain, he had played for FC Barcelona, he was 27, and from the beginning he gave me the feeling that he appreciated me, the rookie.
“I was the defender, he the goalkeeper: he literally stood behind me.”
The World Cup winner added, “He encouraged me, I would go my way, he pointed out my qualities – which one sometimes no longer sees himself as an insecure 19-year-old.
“He let me feel that he felt safe with me in the defense. I think a more beautiful experience can hardly be done at work, no matter what job you do: he gave me his trust.”
Mertesacker, who will retire at the end of the season to take up a job in Arsenal’s academy, went on to discuss his shock as he learned of Enke’s death.
“The news of his death hit me all the harder. How was it possible that this well-balanced, reflected friend had apparently been so ill that he took his own life?
“How was it possible that I did not notice? And, of course, the question hurt: Why had he never told me about his depression? We were friends who, as they say, told everything.”
You can read the full post on Theresa’s blog, here.