Ant reunited with Dec for first day back at work on Britain's Got Talent
The presenter, who stepped away from his TV roles last March after a drink-driving arrest, smiled alongside his presenting partner in an Instagram photo shared on their joint page.
The caption read: "#BGT 2019. Audition day 1. The boys are back in town!"
McPartlin and Donnelly were pictured in a selfie in the back of a car, seemingly before arriving at the London Palladium for the first day of auditions on the ITV programme.
After arriving at the back entrance of the theatre in an SUV they greeted fans, but did not answer questions from the media.
Last year, Donnelly hosted the live Britain's Got Talent shows solo, although McPartlin had appeared in the pre-recorded audition episodes.
McPartlin, 43, stepped down from presenting Saturday Night Takeaway following his arrest for drink-driving and returned to rehab.
Donnelly later fronted I'm A Celebrity... Get Me Out Of Here! with Holly Willoughby instead of McPartlin.
The reunion was greeted with delight by Willoughby who tweeted: "Woooohooooo!"
McPartlin, who divorced wife Lisa last year, previously struggled with a two-year addiction to super-strength painkillers following a knee operation.
He was later banned from the road for 20 months and fined £86,000 for driving while more than twice the legal drink-drive limit.