Jason was snapped leaving Kylie’s bash which was held at one of London’s trendiest nightspots – the Chiltern Firehouse.
The 49-year-old merged looking somewhat dishevelled with a stain on his white jeans, which were partially unzipped.
With a guest list that would make the rest of us weep with envy, Kylie wore a stunning metallic gown by Stella McCartney for the occasion and sang along with pop royalty Rick Astley as he performed his hit song Never Gonna Give You Up.
Other stars attending the party included fellow Neighbours star Guy Pearce, comedians Alan Carr, David Walliams and Kathy Lette, rocker Chrissie Hynde and fashion designer Patrick Cox.
Kylie herself marked her milestone birthday by tweeting a picture of herself posing naked behind an ornate, embellished guitar.
‘And so a new decade begins. How thankful I am for the opportunities life has afforded me. 50..... Let's go!’ the superstar captioned the picture.
Speaking previously about her attitude to towards turning 50, Kylie said: ‘How do I fit in the world of pop at 50? I know I’m not young, but I’m not old.
‘A kid will think that I’m old. An older person will think I am young. It’s all relative,’ she added.
Kylie’s sister Dannii also tweeted her congratulations ahead of the big day.
‘My big Sis. 50 fabulous years I’m so proud to be your sister,’ she wrote alongside three dancing emojis.
‘Everyone is celebrating this special birthday with you. Parteeeeee time.’