Six-time Grand Slam winner Boris Becker revealed that he will coach sixth-ranked Holger Rune for the rest of the season.

Becker told Eurosport on a podcast published Thursday that he will start working with the 20-year-old Danish player at next week’s Swiss Indoors.

Becker, 55, was released from prison last December after serving eight months for illicitly transferring large amounts of money and hiding assets after he was declared bankrupt.

“It makes me a little proud that he asked me. The contact has existed for a long time. Now it was a very good fit,” Becker said. “My calendar allows it and I have always been interested in Holger because he is on the tennis court with so much commitment and temperament.”

Becker, who coached Novak Djokovic from 2014-16, said he would focus on the mental aspect of tennis with Rune, whom Becker called “a rough diamond that needs polishing.”

Rune, who was No. 4 in August, is the highest-ranked Danish male player ever but has won just once since losing to then-world No. 1 Carlos Alcaraz in the Wimbledon quarterfinals in July. Rune also reached the quarterfinals at the French Open for the second straight year in June.

“I have known Boris for a long time,” Rune recently told Danish channel TV 2 Sport. “He follows tennis a lot in general and he has written to me a few times. Also when I was a little younger, he gave me some tips and tricks. There he showed that he supports me.”

–Field Level Media