As we previously reported, JB had shown interest in purchasing the Two And A Half Men actor's $10.8million home - which Kutcher had been renting following his split from wife Demi Moore - for himself and girlfriend, Selena Gomez.
Now, Ashton has revealed in an interview on ABC's Jimmy Kimmel Live that he had to splash the cash on the property after he found out Biebs had viewed the mansion.
Appearing alongside the 18-year old heartthrob to promote the new series of hit MTV show Punk'd, the 34-year old explained: "I had to buy the house because I thought he was going to buy it out from under me.
"I was like 'I don't want to lose this house'. He forced me to buy a house. He's trying to steal my swagger,"
Kutcher went on to disclose how he found the stunning house online, explaining: "I've been living on this internet service for like a year - well, since November.
"I started living on this service called Air B&B, where you can basically go online and rent a house or a room in a house. It's sort of like travelling around the world, living on this service.
"I knew I had to come back and do Two And A Half Men in January so I found this amazing house in LA that was on Air B&B and I booked this house to stay in for three months. I was away, I booked the house, it was all done."
He continued: "All of a sudden my assistant tells me there's somebody coming to look at the house to maybe buy it."
Gesturing at Justin, he laughed: "I get a text from this guy and he's in my house, checking it out, trying to buy my house.
"He's like 'Yo, I'm in your house right now. I'm checking it out'. I'm like 'What? Are you trying to take my house from under me?' Then he's like 'Don't pay any more than nine five for it'. He's like my big brother, giving me real estate advice."
Kimmel then suggested that maybe Ashton and Justin could be roommates, to which Kutcher joked his LA pad was for over-21s only.
Bieber then said with a smile: "I'm 18. I could be almost ready. You could train me. We'll wait a couple of years,"
Watch MTV News on the hour every hour on MTV - Sky Channel 126 and Virgin Channel 134