Olivia Newton-John shares a birthday duet with longtime friend Cliff Richard

Can you believe Olivia Newton-John is turning 71 today?!

While the past year has been a difficult time for the iconic Aussie star - who is currently undergoing treatment for stage 4 breast cancer - we're celebrating her special day with a throwback video from 2015, when she reprised her 1980 duet with close pal Sir Cliff Richard.

The pair - who have been friends for over 40 years - took to the stage at London's Royal Albert Hall to perform 'Suddenly', from the soundtrack Xanadu.  

READ MORE:
• The cast Of Grease: Then and now
• John Travolta teases fans by saying him and Olivia Newton-John are "trying to do something together"

Newton-John was previously diagnosed with breast cancer 25 years ago in 1992, after finding a lump on her right breast.

The 'Psychical' hitmaker - who has a daughter Chloe with her ex-husband Matt Lattanzi - underwent a partial mastectomy and six months of treatment, before getting the all-clear.

However, there was more heartache for the star when she was diagnosed with cancer in her shoulder in 2013 after she was involved in a minor car accident.