"When that's not what you do for a living, it's a little intimidating at first."
One of the commercials - showing Doug at home shooting hoops, cooking lasagne, building a bird house and chilling out in his man room - went viral on YouTube, notching up more than one million views.
Doug says "a whole bunch" of it was artistic license and was designed to be tongue-in-cheek.
The humour was actually what got him on board in the first place.
"I thought their idea was funny. And so from a humour side that probably got my interest,'' he says.
He ran the idea by Brad, who thought it was funny too and told him to go for it.
As for what Brad thought of the commercial: "He thought it was hilarious" and the rest of their family have "made sport of it as well (and) had a little fun at my expense".
Doug says the whole experience has been nothing but enjoyable.
"We're just having fun and a good time," he says.
"I've seen what obviously Brad, for years, what they go through and I'm getting all the good stuff."
Doug's also grateful to Virgin boss Richard Branson for helping out a charity he set up two years ago that gives aid to underprivileged school children.
"Virgin Mobile made a nice contribution to Care to Learn, one of my charities in Missouri, so that was really great," he said.
As for whether Doug thinks he'll follow in his big brother's footsteps and try the acting route, he said he's enjoyed stepping outside his comfort zone, but had no plans.
"This wasn't planned and I can't say I have any more but at the same time..."
So, hypothetically, if he could have, which of Brad's movies would he like to have been in?
"That's a tough one," he says.
"I love Inglourious Basterds as a movie, so probably somewhere in there.
"Maybe not his part, maybe just one of the Basterds."
Watch Doug Pitt's ad below:
- AAP