Bleakley became a household name when she was chosen to replace established star Myleene Klass on the early evening magazine show in 2007.
Now BBC bosses hope to repeat the successful formula by replacing Bleakley - who is set to present ITV's new early morning show Daybreak - with another fresh face, Alex Jones.
Jones, 32, is an experienced presenter but is barely known outside her native Wales.
Bleakley, who learned her television skills in Northern Ireland, was also barely known in the rest of Britain until she landed a seat on The One Show sofa next to Adrian Chiles.
Her fresh face and bubbly personality, along with her on-screen chemistry with Chiles, who will work with her on Daybreak, proved a hit with viewers and BBC bosses hope Jones and comedian Jason Manford will be a similar success.
Jones even has an uncanny resemblance to Bleakley and both had long dark hair until Jones cropped hers into a sharp bob recently.
The Welsh presenter, a former girlfriend of 101 Ways to Leave a Gameshow presenter Steve Jones, said: "I'm absolutely thrilled to bits to be joining The One Show.
"I watch the show at home every night on my sofa and can't believe I'm now swapping it for The One Show sofa.
"It is the break I have only ever dreamed of and can't believe I'm getting to work with Jason Manford, who I think is just fantastic - it truly is the icing on the cake."
Manford said: "After meeting so many brilliant presenters Alex just felt really special.
"She is going to be brill and we can't wait to start the show together."
Jones, who is fluent in Welsh, has worked in television for 10 years and presented travel series Tocyn, style show Salon and Chwa, a Welsh language extreme sports series, for the channel S4C.
She also co-hosted Jonathan with former rugby player Jonathan Davies during the 2010 Six Nations Championship and is a regular co-host on Real Radio GMG in Wales.
The One Show editor Sandy Smith said: "Alex is warm, funny and very experienced despite being almost unknown outside Wales.
"It feels right for many reasons to be developing someone new at this time and I hope One Show viewers enjoy seeing her relationship with Jason develop on screen and take her to their heart."
Daytime Controller Liam Keelan said: "Her screen test with Jason was outstanding and from that moment we knew she was the one.
"She has a lovely sense of humour and she's the perfect fit for Jason Manford."
Manford and Jones take over The One Show, which regularly attracts more than five million viewers, from August 16 and will host it every Monday to Thursday with Chris Evans taking over on Fridays from August 20.
The decision to draft in Evans one day a week was said to have been part of the reason that Chiles quit in April for a new four-year deal with ITV.
Chiles said working on the show had been "an absolute ball" but that hosting ITV's World Cup coverage as a result of the channel change was his "dream" job.
Bleakley later said she was "torn" between staying with the BBC or following Chiles to ITV to resume their successful on-screen partnership.
Her hand was forced in June when the BBC withdrew its offer of a new contract, saying the uncertainty could not continue and it was not prepared to enter a bidding war.
Chiles and Bleakley, who now share a management company, will front Daybreak from September.
The shake-up of ITV's early morning broadcasting has prompted the departure of GMTV regulars Emma Crosby, Andrew Castle, Ben Shephard, Penny Smith, Carla Romano and Richard Arnold.
GMTV anchor Kate Garraway will stay on, becoming Daybreak's entertainment editor, and will be joined by Steve Hargrave as entertainment correspondent.
Veteran broadcaster John Stapleton, correspondent Richard Gaisford and Dr Hilary Jones are also staying.
Lorraine Kelly will present a revamped follow-on show to Daybreak live from a new studio from September.
Comments