The story goes that Rafael Nadal's mother does not recognise her son with a racket in his hand. The man who raised the benchmark for athleticism and intensity on a tennis court simply bears no resemblance to the boy who still lives in the apartment above her own back home in Mallorca.
Relentless, ruthless and at times indomitable, over the years Nadal has conquered all four grand slams, anchored Spain to Davis Cup glory, laid claim to an Olympic gold medal and successfully dethroned Roger Federer as the dominant force in men's tennis.
And yet the minute he steps off the turf, dirt or concrete, Nadal is a figure transformed. The full-bodied fist pumps are replaced by mild-mannered press conference platitudes, the snarls and glares by smiles and broken English.
It is not an act - or at least, not in the way you might imagine. The young man who dreams of fishing in the Mediterranean once he retires is the Rafa known to friends and family. The supercharged baseliner who has collected titles on all continents and surfaces is the Nadal the rest of us see, the topspin-crazed Hyde to his off-court Jekyll.
So perhaps we shouldn't be surprised to hear the Spaniard downplay expectations on his return after a seven months spent rehabilitating those famous knock-knees, in spite of his early successes.
In truth it's too soon to know what to make of Nadal's comeback. On the one hand, he has reached the finals of his first two tournaments, coming within a tiebreak of winning the VTR Open in Chile and handling David Nalbandian in straight sets at the Brasil Open in Sao Paulo.
But he is yet to face a player ranked in the world's top 25. He has only played on clay, knowing that both his joints and his confidence could be jarred by returning to the hard courts too soon. As for five-set encounters, we will not know until he returns to Paris in search of an eighth French Open title.
And then there is Nadal himself, haunted by each niggle in his knee and refusing to look beyond the next tournament. "If my knee is in pain, I can't move," he said after beating Nalbandian. "If I can't move well, I can't hit the ball properly. If my knee is not in pain, it allows me to hit the ball more properly and the game intensity increases, and that was what happened today. Of course, David made some mistakes but, in general, this was my best game."
He's been here before, of course, foregoing the chance to defend his 2008 Wimbledon title after suffering his first ever defeat at Roland Garros against Robin Soderling in 2009. Back then he made a gradual return to the upper echelons, producing an unlikely run to the semi-finals of the US Open before bowing out tamely to eventual champion Juan Martin del Potro. Within a year he had three of the four grand slams to his name, adding a maiden triumph in New York to his French Open and Wimbledon crowns.
Cause for optimism, perhaps - or maybe not. In 2009 Nadal made his comeback on the hard courts of Montreal before playing in Cincinnati and then at the US Open. The rest of the season was played on the hard stuff, and Nadal was there, fitting in seven tournaments before finally returning to clay for Spain's Davis Cup victory over the Czech Republic.
This time, clay has virtually become a prerequisite for his participation. He was not ready for Doha (hard) and therefore the Australian Open (hard), before heading to make his comeback in South America. The greater caution suggests he is dealing with a more serious injury, something that could genuinely threaten his career.
So will he play in the first Masters 1000 events of the season in Indian Wells and Miami? "I think of Acapulco and nothing else," he told reporters in Sao Paulo. "We are not in a position to think weeks ahead. We'll go day by day, week by week.
"Let's see how my knee responds in Acapulco, we will discuss when we finish all this clay court [swing] what has happened during these three tournaments and what I thought about it. Then we will see if we are ready to play in Indian Wells or not. It is not a matter of better rivals or surface, is a matter of how my knee is progressing."
"I have no problem playing against better opponents," he added. "I accept losing or winning. I understand that it's been a long time since I competed at the highest level. I have had only had two weeks getting rhythm, but I need time to continue to improve and become competitive."
Then again, this is Rafa speaking, not Nadal. Rafa accepts losing or winning - Nadal does not. Rafa is not looking beyond Acapulco - Nadal is intent on winning an eighth French Open. The worry is that Rafa starts turning up on court, whispering in Nadal's ear, allowing the fear of further injury to prevent him from scaling the heights that these past two weeks - and all that has gone before - suggest are still within his grasp.
Nadal still turns up with a racket in his hand. Sure, this may be his last chance, and that's enough to sow the seeds of doubt in anyone's mind. But as his knees improve mental fortitude will follow, and a mother will once again be left wondering what happens to her son when he steps onto a tennis court.