The 65-year-old said it was a "huge pleasure" to be back on the television as he hosted the show for three days alongside his former BBC Breakfast colleague Susanna Reid.
"Big thanks to @susannareid100, everyone @gmb, and all those watching who sent such lovely messages this week.
"A huge pleasure to be back on the telly. Thank you for having me," he wrote on Twitter.
As he signed off on the programme today, Reid remarked: "It's been magic having you."
Earlier this week, fans had expressed their delight at seeing the pair back together again
Turnbull, who currently presents his own radio show on Classic FM, shared in 2018 that he had been diagnosed prostate cancer.
Reid has been fronting the breakfast show alongside several different presenters Monday to Wednesday since Piers Morgan left earlier this year.
Watch: Bill Turnbull makes risque joke during GMB stint with Susanna Reid
His exit came as he refused to apologise for comments made about Meghan Markle's interview with Oprah Winfrey.
The journalist said he did not believe claims made by the Duchess of Sussex, who had made remarks about her mental health and experiences of racism in the chat.
A permanent replacement has not yet been announced, but the likes of Adil Ray and Alastair Campbell have occupied the desk in his absence.
Morgan mocked Campbell for accidentally implying the Queen had died during his stint, describing it as the "worst gaffe in breakfast show history".
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