Angus Lake, 42, pleaded guilty to driving under the influence. He did it just 10 minutes before his trial was set to start. He will be sentenced March 15.
Lake faces up to 14 years in prison.
Last April, 25-year-old trainer Michelle Eustis and another woman left a gathering at Balmoral to go ride a horse. Lake went looking for them and crashed his car into their horse, killing Eustis and seriously injuring her friend.