Rafael Nadal has revealed he sent a private message of congratulations to Roger Federer via text after the Swiss’ remarkable 20th Grand Slam title win at the Australian Open. The world No. 1, who was forced to retire during his epic quarter-final match-up with eventual runner-up Marin Cilic, admitted he kept his praise for the 36-year-old out of the public sphere as he does for people he knows well. Federer became just the fourth tennis player – male or female – to his the 20-mark for Grand Slams won, and the only star to have achieved the feat playing best-of-five-set format. MORE: TENNIS History shows Roger Federer’s return to world No. 1 in Rotterdam is no guarantee Roger Federer on brink of history as he sets sights firmly on Rafael Nadal Nastase has ‘sexual harassment’ & ‘racially insensitive comments’ ban reduced Federer won the Australian Open (Picture: AFP/Getty) And Nadal, who has an impressive 16 Slams to his name, sent his long-term rival a message of congratulations. ‘I congratulated him privately through a text message,’ Nadal revealed at a fan Q&A. ‘With people I know, I do it more privately than publicly.’ Nadal was forced to retire against Cilic (Picture: Getty) Federer’s defence of his Australian Open title has given him the opportunity to return to world No. 1 for the first time since October 2012 in February as he closed the gap on Nadal to just 155 points. The Spaniard will lose top spot in the rankings if he fails to recover from injury in time to compete in Acapulco, which begins at the end of the month. However, he is thought to be confident of fulfilling all his schedule obligations in the coming period, and signed up to Queen’s as a warm-up event for Wimbledon.