Rees celebrates his world title with trainer Enzo Calzaghe

The bout will be held at the Cardiff International Arena on 22 March.

"It took so long to win this title, I'm not giving it up first fight," said Newbridge's undefeated Rees, 27, who beat Souleymane M'Baye for the crown.

German-based mandatory challenger Kotelnik, 30, has an impressive record of 28 wins (12 knockouts), two losses and one draw.

The draw came against then-champion M'Baye in Liverpool last March, while Kotelnik's only defeats are points losses to Junior Witter and Gabriel Mapouka.

Rees, who won the title in Cardiff last July, is trained by Enzo Calzaghe and has a record of 27-0 with 13 knockouts.

"Beating M'Baye was a massive shock to many people - but not to me," said Rees.

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"Now I'm going to build on the win and become a unified world champion like my friend Joe Calzaghe.

"What Joe has done over the years has been amazing and a real inspiration to boxers in Wales, and when he finally retires, I'm going to take up where he left up.

"Kotelnik's got a great record, but I'm going to jump on from the first bell and give him hell.

"I didn't let M'Baye have a moment's rest, and I'll be all over Kotelnik right from the start."

On the undercard, Gary Lockett appears in an international 10-rounder as he aims to keep up the pressure on full WBO champion Kelly Pavlik, while Barrie Jones and Tony Doherty meet in a challenge for the Welsh welterweight title.