Noel Edmonds has returned to national radio after a 20-year absence.
Noel Edmonds was on BBC Radio 1 from 1969-83
BBC Radio 2 called on Edmonds, a former BBC Radio 1 breakfast show host, because current DJ Johnnie Walker will be away for two months to have cancer treatment.
Edmonds, who now heads his own broadcasting company, is presenting the two-hour Drivetime show from 1700 BST.
"I'm really delighted to be here but I'm extremely unhappy about the circumstances - I wish Johnnie well with his treatment," he told listeners on Monday.
"You've got me until October - please be gentle - it's a quarter of a century since I last hosted a [daily] radio show.
"Boy oh boy, am I glad to be back."
He added that it was a "great opportunity" and he was "very excited" to be back behind the microphone.
Walker has been diagnosed with non-Hodgkins lymphoma
Edmonds left the BBC three years ago, calling the programmes "too boring", after having TV success with the Late Late Breakfast Show, his House Party and Telly Addicts.
In June, Walker - also a former Radio 1 star - revealed he had been diagnosed with non-Hodgkins lymphoma.
He described it as "a toughie" but added that it was thought to be a very treatable form of the disease.
Radio 2 controller Jim Moir said: "I join Noel in wishing Johnnie a swift recovery and return to the airwaves.
"In the meantime, Noel is one of the UK's most successful and innovative broadcasters and we are delighted that the drivetime show will be in such capable hands."