This Jan. 12, 2013 photo shows Mirka, right, wife of Switzerland's Roger Federer watches with her daughters Myla and Charlene and a unidentified woman during a exhibition match during the Kids Tennis Day at Melbourne Park ahead of the Australian Open tennis championship in Melbourne, Australia. Federer announced on Twitter that he and his wife are expecting another child next year.  [Photo/Agencies]

Already in the swing of parenting, Roger Federer is getting ready for a larger family.

The tennis star says on Twitter that he and his wife, Mirka, are expecting another child next year.

Twins Charlene and Myla were born in July 2009, and Federer wrote Wednesday, "Mirka and I are very happy to share the news" that the couple's daughters "will be big sisters in 2014!"

Federer's agent, Tony Godsick, confirmed to The Associated Press the tweet is legitimate.

The 32-year-old Federer has won a record 17 Grand Slam singles titles and spent more weeks at No. 1 than anyone else in the history of the ATP rankings.