Image caption Dermot O'Leary completed a 24-hour dance marathon for Comic Relief earlier this year

Dermot O'Leary has stepped in to replace Sir Terry Wogan as host on Friday's Children in Need fundraiser.

Sir Terry 77, had to pull out - for "health reasons" - for the first time since the TV event's launch in 1980.

The veteran TV presenter is having a procedure on his back and is understood to have withdrawn in line with doctors' advice.

He said he would miss "our wonderful, inspiring evening" but would still be "watching, cheering and donating".

O'Leary will front the annual charity BBC show from 19:30 - 22:00 GMT.

"We are incredibly grateful to Dermot for stepping in at such short notice but know he'll do us and Sir Terry proud," the corporation said.

The show is also due to be presented by Tess Daly, Rochelle Humes, Nick Grimshaw and Fearne Cotton.

"It's a huge honour to be asked to step into Sir Terry's shoes tonight; he is one of my broadcasting heroes and has been a source of support for me down the years," O'Leary said.

Image copyright PA

"I'd like to add my best wishes to Sir Terry for a speedy recovery, and I hope I do him justice and do my small part to make the night a success and make as much money as we can for disadvantaged children across the country."

'Do you proud'

Sir Terry said the event - which this year is set to feature a special Star Wars sketch with characters C3PO and R2-D2 - would go on "bigger and better than ever".

One Direction, actress Dame Helen Mirren, former Doctor Who star David Tennant, Sherlock actor Martin Freeman and singer Ellie Goulding are also expected to feature in the show.

Singer and television presenter Humes tweeted, telling Sir Terry to "Get well soon", and that "we will miss but will do you proud".

Image copyright @BBCCiN

Image copyright @RochelleHumes

In a statement, Sir Terry said: "So here we are on the 36th edition of Children in Need, every one of which I've been proud to present since it started in 1980, and for the first time I won't be there to cheer you on with word and gesture to another record-breaking year."

He added: "The British public, as always, will dig deep in their pockets and purses to help the country's disadvantaged children, knowing that every penny will go to those who need it most."

Media playback is unsupported on your device Media caption Sir Terry presenting last year's Children in Need

A BBC spokesman said: "We are so sorry that Terry won't be with us as we know how passionate he is about Children in Need.

"But we wish him a very speedy recovery and know he'll be watching from home and enjoying the show."

Children in Need has raised more than £790m for children and young people across the UK since its launch.

More than £32.6m was raised on the night of the broadcast last year.