Can my brother and I both claim Mom?

The past 2 1/2 years my brother and I share cared for my mother. she lived with him 4 days per week and me 3. The last 4 or 5 years he has claimed her as a dependent on his taxes. She moved in with me FT permanently in Sept. We told our accountant the truth and claimed her on our taxes for this year. Can we both claim her ? He is having a fit and blaming me for him having to pay a lot of $ to the IRS. I think he's nuts.