Princess Mary hits the dancefloor and rocks out at a private concert with her family to celebrate son Christian’s 18th birthday in Christiansborg Palace

Crown Princess Mary proved she still knows how to party with the royal family as she celebrates her eldest son Christian’s 18th birthday in style at Christiansborg Palace on Saturday.

Mary was dressed for the occasion in a sparkling black floor-length dress, completing the look with a stylish updo, her wedding diamond tiara and a royal blue sash.

But the formal look didn’t stop her from getting involved when Queen Margrethe unveiled her grandson’s birthday surprise: a private rock concert at the palace.

The Tasmania-born princess and mother of four clapped and grinned enthusiastically on stage where popular Danish rock star Benjamin Hav jammed with his band The Family.

The 51-year-old’s family followed suit and seemed equally impressed by the surprise performance as they showed off their best moves on the dance floor.

Crown Princess Mary proved she can still party - as she celebrated her eldest son Christian's 18th birthday at Christiansborg Palace on Saturday

Crown Princess Mary proved she can still party – as she celebrated her eldest son Christian’s 18th birthday at Christiansborg Palace on Saturday

Crown Prince Fredrick, who was dressed in full ceremonial dress complete with his traditional blue sash displaying his medals, also danced up a storm that night.

Prince Christian could barely contain his excitement and flashed a wide grin as he shook his head wildly to the beat of the music.

His little brother Prince Vincent, 12, bounced next to his brother and enjoyed the big birthday party.

The young people were joined at the party by other European royals.

The concert followed the prince’s official gala dinner and balcony appearance with his parents and the queen.

Prince Christian took the stage during the concert

Prince Christian took the stage during the concert

A video of the concert was posted on the palace’s official Instagram, thrilling the Danish public.

And a photo shows that the birthday prince was able to jump on stage and take over the microphone.

‘I am so proud of our royal family. Beautiful young people, what an experience you have had for a lifetime. What a party,” someone said in awe.

Some criticized the prince’s moves.

His little brother's joy was also captured on camera

His little brother’s joy was also captured on camera

“Prince Christian may be king, but Vincent is king of the floor,” said one fan.

Others said the Queen did herself a good job by performing the concert.

‘The greatest queen in the world!’ others cheered.

‘How cool is Queen Margrethe…. Cool gift for the guests.’

‘A beautiful gift from a sweet grandmother. She knows how to capture and retain youth.’