The pair fronted BBC Breakfast together until 2014, when Reid left the show to join ITV.
Turnbull then left BBC Breakfast in 2016, just two years before confirming he'd been diagnosed with prostate cancer, which he discussed on Monday’s (24 May) episode of GMB.
But what is Bill Turbnbull’s presenting background and what did he say about his cancer treatment?
Here’s what you need to know.
Who is Bill Turnbull?
Bill Turnbull began his career at Scottish local station Radio Clyde in 1978, before joining the BBC as a reporter for the Today programme in 1986 and Breakfast Time as a reporter in 1988.
He then became a correspondent for BBC News in 1990, before becoming one of the main presenters of BBC Breakfast from 2001 to 2016, initially presenting with Sian Williams, and then later with Sarah Montague, Mishal Husain and Susanna Reid.
He has also presented the religious series Songs of Praise and game show Think Tank.
Turnbull - who now works on Classic FM - previously filled in for Reid’s former co-star Piers Morgan on GMB last year, but will be back in the presenting chair to host alongside Reid from Monday 24 May until Wednesday 26 May.
Bill is one of a string of guest presenters to join Reid after Morgan quit the show in March.
Turnbull said: “I am very pleased to be back presenting on GMB, especially as I get to be reunited with my old pal Susanna.”
Reid added: “I am delighted Bill is back in the presenter chair at the GMB desk. He has been a beloved favourite of breakfast television viewers for years and a good friend of mine.”
Neil Thompson, editor of Good Morning Britain, said: “I’m thrilled that Bill is rejoining us behind the GMB desk.
“It’s not just his brilliant and enduring onscreen partnership with Susanna that makes its mark, it’s his relationship with the audience in general, one based on authenticity, authority, warmth, humour and trust.”
What did Bill Turnbull say about his cancer treatment?
In 2018, Turnbull announced that he had been diagnosed with prostate cancer, and he discussed his current treatment during Monday’s episode of GMB.
The broadcaster, 65, was told by doctors in 2017 that he had incurable prostate cancer, which has since spread to his spine, ribs, pelvis, hips and legs.
In 2019, Turnbull told Prostate Cancer UK: “When you’re diagnosed with prostate cancer it can be a pretty scary moment. It was for me. Particularly because it had already spread to my bones and the long-term outlook wasn’t good at all. It was a big shock for me and for my family, and we had some pretty dark times. But luckily, I started treatment very quickly after my diagnosis.”
During Monday’s episode of GMB, Turnbull explained that he now has to have a radioactive isotope injected into him once every six weeks.
"It makes you so live, so to speak, that I have to sleep in a separate room for three days, no prolonged contact with small children or pregnant women for six days," he said.