Vorderman is leaving Countdown after 26 years on the show
Presenter Carol Vorderman has announced she is to step down from Channel 4 game show Countdown.
The 47-year-old has worked on the word and maths show since it began in 1982, initially alongside Richard Whiteley.
When Whiteley died in 2005, she continued to co-present with Des Lynam and latterly Des O'Connor. He announced on Wednesday he was quitting the show.
Vorderman's manager said she did not think she could go through the process of bonding with another co-presenter.
Countdown was the first programme seen on Channel 4.
The network's director of television Kevin Lygo said he was "extremely sorry to see Carol leave".
"She was the first woman on Channel 4 and has made an enormous contribution to the success of Countdown over the last 25 years," he said.
"We hope to work with her again on other projects."
Nearly 5,000 episodes of the quiz show - a mixture of word games and mathematical problems - have been filmed.
'End of an era'
With a high IQ as well as degrees in engineering, Vorderman was seen as a natural to calculate complicated mathematical problems on the programme.
In a statement, Vorderman's manager John Miles said she considered quitting the show when Whiteley died but eventually agreed to continue.
However, he added that she did not think she could go through the process of bonding with another new co-presenter and "just feels that it is time to leave".
He said: "Countdown has been such a huge part of her life for so long.
"Carol wants to thank all of the crew, the thousands of contestants who have played the game and the millions of Countdown viewers, for whom she has the greatest respect.
"She is extremely sad."
Another Countdown regular, lexicographer Susie Dent, said the news was "devastating" for the show.
"It's the end of an era for Countdown, and it's the end of an era for me - Carol has been my colleague, my mentor, and my friend for over 15 years," she added.
"She and Richard together made one of the strongest and enduring shows television has ever seen, and also built one of the closest teams."