Alexander Zverev falls to Roger Federer in the Gerry Weber Open final on Sunday in Halle.

Roger Federer celebrates his ninth Gerry Weber Open title in Halle.

Roger Federer tries to win his ninth title at the Gerry Weber Open in Halle.

Roger Federer takes on Alexander Zverev in the Gerry Weber Open final.

Just about everyone is a fan of Roger Federer in Halle.

Roger Federer is through to his 11th final in Halle.

Roger Federer reaches his 11th Halle final on Saturday at the Gerry Weber Open.

Roger Federer battles past #NextGenATP Karen Khachanov in the Halle semi-finals on Saturday.

Roger Federer is two matches away from a ninth title in Halle.

Roger Federer is through to his 15th quarter-final in Halle.

Roger Federer remains in pursuit of a ninth title in Halle.

Dominic Thiem, Philipp Kohlschreiber, Tournament Director Ralf Weber and his wife Irina, Roger Federer and Boris Becker enjoy the players' party Tuesday night at the Gerry Weber Open.

Roger Federer rolls during his opener at the Gerry Weber Open in Halle on Tuesday.

Roger Federer couldn't make good on a match point against Tommy Haas in Stuttgart.

Roger Federer will compete next at the ATP World Tour event in Halle.

Roger Federer suffered his first opening-round defeat on grass since 2002.

Long-time friends Roger Federer and Tommy Haas embrace at the net after Haas' upset win on Wednesday in Stuttgart.

Roger Federer returns to tour-level action on Wednesday at the MercedesCup in Stuttgart.

Roger Federer and Tommy Haas have some fun at the Schlossplatz ahead of the MercedesCup in Stuttgart.

Tommy Haas and Roger Federer have fun on Monday at Schlossplatz, the largest square in Stuttgart, ahead of the MercedesCup.

Roger Federer and Tommy Haas have fun at Schlossplatz, the largest square in Stuttgart, on Monday ahead of the MercedesCup.

Roger Federer returns to tour-level action at the MercedesCup in Stuttgart.

Roger Federer and Tommy Haas play mini tennis at Schlossplatz in the centre of Stuttgart.

Roger Federer and wife, Mirka, attend the 'Rei Kawakubo/Comme des Garcons: Art Of The In-Between' Costume Institute Gala at the Metropolitan Museum of Art.

Roger Federer celebrates his third Miami Open title with coach Ivan Ljubicic, whom he defeated in the Miami title match in 2006.