Former world No. 9 Andrea Petkovic says it is impressive how Rafael Nadal managed to go from someone fans didn't like very much early on because he was a major challenge to Roger Federer to also becoming a fan favorite.

Although the relationship between Rafael Nadal and Roger Federer appears to be peachy on the outside, the pair are far from being pen pals despite ditching their differences

Tennis legend Roger Federer wrote a heartfelt letter to Rafael Nadal on Tuesday before the Spanish star joins him in retirement. Nadal is participating in the Davis Cup in Malaga, Spain this week before saying goodbye to the sport he has played professionally since 2001.