A tattooed YouTuber is replacing Rachel Riley on Countdown in a shock shake-up and has announced the appointment to fans with photos from the Channel 4 set.

A change from the usual glamorous number expert Rachel, 39, Cambridge and Oxford university mathematics boffin, Dr Tom Crawford, will be taking her place while she has a break from the show. 

Used to being behind a camera, Dr Crawford has made a name for himself with his impressive intellect and maths skills that he shows off on his YouTube channel.

Racking up over 200,000 subscribers with his question solving videos on Tom Rocks Maths, he also has 22,000 followers on Instagram.

Some of his videos have racked up millions of views and he regularly posts clips of himself tackling exams or discussing math-related topics. 

And now, the mathematics geek will stand behind Channel 4's cameras when he features on Countdown for the next three weeks.

After teasing fans earlier in the week with a upcoming 'ridiculous announcement', Dr Crawford confirmed to fans on Instagram yesterday he would be joining the Channel 4 show temporarily. 

He posted a photograph of himself grinning with Rachel, captioned: 'COUNTDOWN. Still can’t believe this happened, but you will now be able to watch me attempting to do maths live on television for the next 3 weeks, starting Monday at 2:10pm on @channel4. 

'@rachelrileyrr - and her unparalleled arithmetic skills - are irreplaceable, but with @mrcolinmurray and @susiedent by my side, we’ll do our very best to keep you entertained for the next few weeks. Long live daytime television!!'

Excited fans rushed to comment their support, with one saying, 'Good luck!. Looking forward to seeing your attempts, which I'm sure will be great.';

'I KNEW IT!'; 'Ooh, this is exciting! I’m sure you’ll be great!';

'This is incredible news! Can't wait to watch. You will be brilliant!';

'Good luck, Tom. You have some big shoes to fill.'; 'This is awesome!'

Perhaps more used to fame than most, the maths genius has made headlines previously for his quirky formulas.

Last year, he calculated the perfect way to tackle an all-you-can-eat holiday breakfast buffet.

And he worked out the best method to get down on one knee and propose.

The mathematician's passion for his subject is so strong he even has related tattoos all over his body.

Earlier this year he posted a photo of his 61st ink which featured 'arithmetic operations'.

He wrote: 'Tattoo #61 - arithmetic operations. Just in case I forget how to do basic maths… They make a great addition to the TRM logo made up of mathematical symbols: 8 4 3 3 ( ).'

Another one featured 'the logistic map' which he described, 'Such a simple function and yet it leads to utter chaos. 

'Mathematically speaking, chaos means apparently random or unpredictable behaviour in systems governed by deterministic laws, which is perfectly exemplified by the bifurcation diagram shown in the tattoo. One of my favourite visualisations in all of maths.'

Very qualified for the new role, Dr Crawford has a PhD in Fluid Dynamics from the University of Cambridge and completed a maths degree at the University of Oxford.

Countdown sees contestants tackle linguistic and mathematical challenges while the clock ticks. 

It first aired in 1982 and is currently hosted by radio presenter and TV star Colin Murray, 47. Susie Dent, 60, also features as the show's lexicographer.

Dr Crawford posted a photo of himself outside of a dressing room on Instagram on Wednesday with the caption: 'Prepare for the most ridiculous announcement coming tomorrow... any guesses as to which TV show I’ll be on? #tomrocksmaths #TVdebut #TVshow.'

The maths boffin is a Fellow by Special Election at Oxford's St Edmund Hall and is a Public Engagement Lead at the university's department for Continuing Education, according to his website.

He also teachers Applied Mathematics at Robinson College.

Rachel has featured on the show since 2009, while Colin joined in 2022 after taking over from Anne Robinson, 80.

Countdown airs weekdays on Channel 4 and is available to stream on channel4.com.