United Kingdom, Oct. 2 -- Robert Irwin has apologised to his mother for ripping his shirt off on Dancing With The Stars.

The 21-year-old star - whose parents are Terri Irwin and late Crocodile Hunter legend Steve Irwin - sent pulses racing this week when he flashed his six pack on the ABC dance competition this week, but now he has admitted Terri and his sister Bindi were watching in the studio at the time.

He quipped: "Sorry, guys, sorry about that!"

After his performance, he joked that the racy display was simply to give the costume team a break.

He teased: "We thought we'd take it easy on the costume department tonight.

"I said to [dance partner Witney Carson], 'I want to bring out cool Robert.'

"I was like, 'He's in there somewh...