He's the former Australian tennis player set to appear on the new season of military-inspired series, SAS Australia.

And on Wednesday, Mark Philippoussis showed off dramatic weight loss weeks after filming the grueling reality series.

Uploading a mirror selfie to his Instagram, the 44-year-old wrote: 'SAS aftermath - never been so excited to watch my ass get kicked,' alongside a flexed bicep emoji.

In the photo, the retired athlete put his taut physique on display.

The post was quickly inundated with comments from his fellow co-stars.

Former Home and Away star Dan Ewing wrote, 'Rigs of SAS calendar has started'.

Sam Burgess who will also appear on the upcoming series wrote: 'Absolute machine'.

Meanwhile, SAS chief instructor Ollie Otterton wrote: 'SAS - Super Ab Solutions!'

'Hope the experience was worth the pain....what an adventure for both body and mind,' one user commented, to which he replied: '100%'.

The series will also star Ironman Jett Kenny, Olympic runner John Steffensen, volleyball champion Kerri Pottharst, Bra Boy Koby Abberton and singer Pete Murray.

Filming for the new series is understood to have already wrapped up, with this year's training camp being in the much warmer location of the Blue Mountains.

Seven decided to ditch last year's location in Jindabyne, where temperatures reach as low as minus three degrees.