Radio 1's chart show host Wes Butters is to leave the station following a reorganisation of it's schedules.
The presenter will leave in February after his contract was not renewed.
Butters will be replaced by JK and Joel who will host a brand new chart show combining the singles count down with the new download and album charts.
The new line up also means Sara Cox returns to host a Saturday and Sunday afternoon show, after taking time off to have baby Lola Anne, born in June.
Before taking a break Cox moved from breakfast to drivetime, but the drivetime show is now longer and Cox said she wanted to be back home in the evening in time to put her daughter to bed.
"I'm looking forward to being back, I've really missed being on the radio," she said.
"I'm going to do my best not to burst into nursery rhymes, although The Wheels On The Bus is an old-school classic."
Radio 1's chart show has come under pressure from rival stations over the last few months.
Radio 1 boss Ben Cooper said: "It's going to be great to have Sara back, and it gives JK & Joel a chance to breathe new life into what remains the biggest single show on the station."