'Couldn't be prouder': The Project's Peter Helliar shares a sweet tribute for lookalike son Liam on his 18th birthday

He's known for his one-liners and self-deprecating humour.

But in an Instagram post on Saturday, The Project co-host Peter Helliar showed a sentimental side.

The 45-year-old comedian shared a photo with his lookalike son Liam, wishing him a happy 18th birthday.

'Couldn't be prouder': The Project's Peter Helliar, 45, shared a sweet tribute for lookalike son Liam on his 18th birthday, in an Instagram post on Saturday (both pictured) 

Peter praised Liam for his empathy and kindness in the post's caption.

'A bit over a decade ago after another ambulance ride to the hospital, after another asthma attack, Liam, who was anaphylactic, said to us: "It's good that I keep getting sick so my brothers don't have to",' the TV star wrote. 

'He has a better understanding of how illness and allergies work now, but he has kept that same kind heart all the way along. 

Heartfelt: 'Smart, empathetic, kind, funny and passionate. Happy 18th Liam. We couldn't be prouder. Love Dad,' the comedian wrote in the post's caption 

'Smart, empathetic, kind, funny and passionate. Happy 18th Liam. We couldn't be prouder. Love Dad.' 

Peter shares Liam with wife Bridget Helliar, who he wed in 2001. They are also proud parents to sons Aidan, 15, and Oscar, 12.

Bridget also posted a sweet throwback photo of a younger Liam to her Instagram page on Saturday, and wrote in the caption: 'Little Liam is 18.'

Family: Peter shares Liam with wife Bridget Helliar, who he wed in 2001. They are also proud parents to sons Aidan, 15, and Oscar, 12 (all pictured) 

Memories: Bridget also posted a sweet throwback photo of a younger Liam to her Instagram page on Saturday, and wrote in the caption: 'Little Liam is 18' 

Peter stars as a co-host on Channel Ten's current affairs program The Project, alongside Carrie Bickmore, Waleed Aly and Lisa Wilkinson.

In May, the comedian said he was 'extraordinarily lucky' to have his role on The Project as his main source of income amid the coronavirus pandemic. 

'I do a fair bit of corporate work emceeing and public and that's all gone this year. And I probably only got through a third of my stand-up tour,' Peter told The Sydney Morning Herald.

'That said, I'm extraordinarily lucky. The Project is my major income.'   

Panel: Peter stars as a co-host on Channel Ten's current affairs program The Project, alongside Carrie Bickmore (centre left), Waleed Aly (far left) and Lisa Wilkinson (centre right)