The 'Green Light' hitmaker - who is currently on her 'Melodrama' tour in Australia - took to her Instagram story on Wednesday (22.11.17) to pay tribute to the 'Partridge Family' star following his tragic death on Tuesday (21.11.17) from organ failure.
The 21-year-old singer uploaded a short video of David playing Keith Partridge in the hit 1970s TV series performing the song 'I Woke Up In Love This Morning' with his co-stars Shirley Jones, Danny Bonaduce, Susan Dey and Brian Foster.
She accompanied it with the caption: ''My first crush. Bye kid.''
She then shared a second video of David wearing a pair of tight purple trousers and a blue T-shirt and claimed her obsession with the singer as a young man is the reason why she has always dated ''skinny boys.''
She wrote: ''Prob the reason I have always dated skinny boys.''
The New Zealand-born singer-songwriter then branded David the ''original teen heartbreaker'' and said she couldn't wait to see him again ''on the other side.''
She explained: ''The original teen heartbreaker. See you on the other side. (sic)''
David passed away at the age of 67 surrounded by his loved ones - less than a week after he was placed in a medically-induced coma at hospital in Florida.
A spokesperson for the star said: ''David died surrounded by those he loved, with joy in his heart and free from the pain that had gripped him for so long. Thank you for the abundance and support you have shown him these many years.''
The 'Could It Be Forever' singer is survived by daughter Katie Cassidy, who he had with Sherry William and son Beau Cassidy, whose mother is his ex-wife Sue Shifrin.
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