Prince Harry and Cressida Bonas Rock Another Weekend
07/08/2013 AT 04:00 PM EDT
The royal and his girlfriend, 24, were at the Mumford & Sons concert at London's Olympic Park Saturday night.
And they liked what they saw.
"They were having a great time and clearly knew the words to the songs as they were singing along," a bystander tells PEOPLE.
After the concert, Harry, 28, had a 20-minute chat with lead singer Marcus Mumford and his wife, actress Carey Mulligan – and shared a hug with the singer.
"They seemed to be getting on really well," Eve Barlow, deputy editor of the music magazine NME tells PEOPLE. "They were very huggy."
The prince also spent time talking to bassist Ted Dwane, who is back performing following his recent brain surgery.
Barlow adds, "Harry and some friends were in a little enclosure behind the stage," she says. "Harry was really unassuming, really chilled-out. They were there for a good hour."
"He was so chilled-out it was possible to think it wasn't him!"
The previous weekend, he and Cressida stayed up late to catch the Rolling Stones and other acts at the Glastonbury festival.
They were also seen partying at a deejay set by Radiohead's Thom Yorke at a special area Shangri-La within the music festival.