thrilled fans when he reunited with his former band member on stage for the first time in over a decade on Saturday.
The 49-year-old singer jammed with , also 49, during his set at the Sandringham House in Norfolk and shocked fans with the surprise guest appearance.
Nodding to their time spent singing – that also featured , 52, Howard Donald, 55, and Jason Orange, 53 – the unlikely duo bashed out their former hit Greatest Day for delighted audience members.
Robbie was performing in the grounds of ’ royal residence which has been transformed into a huge eco-friendly concert venue when he asked his friend to join him.
Equally as excited to be back together as the fans watching the encounter, the stars danced with each other and hugged throughout the live gig.
In true Robbie fashion, he drew attention with his outfit alone, wearing a gold sequined vest over his bare chest and some gold metallic trousers to match.
He accessorised with a white scarf and beamed as he belted out the famous lyrics into his microphone.
Mark appeared a little more low-key in some tailored rouge suit trousers that featured a black button and tucked in a silky black shirt to cover his upper half.
Marking 25 years since the Let Me Entertain You singer went solo and , the show was the final stop on Robbie’s world XXV tour.
Elsewhere across the bank holiday weekend, the event space will host performances from Van Morrison and The Who, as well as a plethora of special guests.
Ahead of the musical extravaganza, Giles Cooper – managing director of Heritage Live – said: ‘We are delighted to have a world-class line-up and the Sandringham concerts are the only two Robbie Williams UK shows for the rest of the year.
‘It was a huge honour to be asked to run five years of concerts at the estate – we know that King Charles III wants to make Sandringham more inclusive.
‘The environmental impact was also very important so we have put together a five-year plan for sustainability to become a leading light for outdoor concerts.
‘We have lots of surprises in store in 2023 and we are praying for good weather – the local community is very excited.’