The movie veteran starred as chimney sweep Bert in the 1964 family film, opposite Julie Andrews as the titular nanny, and he revisited the role on the eve of his age milestone as dancers dressed as his character surprised him with a performance at The Grove shopping mall.

The troupe belted out tracks like Chim Chim Cher-ee and Supercalifragilisticexpialidocious, and Van Dyke gave fans a special treat by stepping in to take part in their closing tune, Let's Go Fly a Kite, much to the public's delight.

The group then sang Happy Birthday to the acting icon to celebrate his big day.

Sharing video footage of the mall surprise on Twitter.com on Sunday (13Dec15), the birthday boy wrote, "I am very grateful that at 90 years old, I can still go out and play!!"

The Grove flash mob surprise wasn't the only public birthday celebration held in Van Dyke's honour - on Sunday, he was given a hero's welcome during a visit to Disneyland in Anaheim, California, where he rode in a special cavalcade as park attendees joined forces to sing and mark his 90th following a dedication ceremony.

Disneyland bosses also presented him with a specially-decorated birthday cupcake.