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 has proven she still knows how to party with the royal  celebrating her eldest son Christian’s 18th birthday in style at Christiansborg Palace on Saturday.

Mary was dressed in a sparkling floor-length black gown for the occasion, finishing the look with a stylish up-do, her wedding-day diamond tiara and regal blue sash.

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

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

The 51-year-old’s family followed her lead and looked equally as impressed with the surprise performance as they pulled out their best moves on the dancefloor.

Crown Princess Mary has proven she still knows how to 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 on the night.

Prince Christian could barely keep his excitement contained and featured a broad grin as he shook his head wildly to the beat of the music. 

His little brother Prince Vincent, 12, was bouncing alongside his brother – enjoying the big birthday bash.

The youngsters were joined by other European royals at the party.

The concert followed the princes official gala dinner and balcony appearance with his parents and The Queen.

Prince Christian took to the stage during the concert

Prince Christian took to the stage during the concert

Video of the concert was posted on the palace’s official Instagram – thrilling the Danish public. 

And a photo shows the birthday prince was able to hop on stage and take control of the microphone. 

‘Am so proud of our royal house. Beautiful young people what an experience you have had for life. What a party,’ one person said in awe.

Some critiqued the princes 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 The King Of The floor,’ one fan said.

 Others said the Queen proved herself well by putting on the concert.

‘Greatest Queen in the world!” others cheered. 

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

‘A good present from a lovely grandmother. She knows how to catch the youth and hold on to them.’