The show’s maths whizz Rachel Riley took to Twitter to react to the news, saying that the addition was “well worth the wait”.
Rachel took to Twitter to compliment national icon Stephen in view of her 695,600 followers by replying to his tweet, which read: “After a 20 year gap, I’ll be guesting on @C4Countdown all this week.
Stephen also tagged Rachel and Dictionary Corner star Susie Dent, 57, in his exciting announcement to his 12.4 million followers.
Reacting to Stephen’s first day of guesting on the show, Rachel wrote: “Worth the wait! (heart emoji)”.
Express.co.uk has contacted the BBC for comment.