Mary-Kate Olsen had a low-key birthday celebration on Saturday with her twin sister, Ashley, a source tells ET. According to the source, Mary-Kate is currently "laying low" amid her split from her estranged husband, 51-year-old Olivier Sarkozy. The source also says that Mary-Kate is not staying at the Bridgehampton home she shares with Olivier. Mary-Kate and Olivier -- the half-brother of Nicolas Sarkozy, the former president of France -- got married in November 2015, three years after they started dating. For more on Mary-Kate and Olivier's split, watch the video below:Reporting by Darla MurrayRELATED CONTENT:Inside Mary-Kate Olsen and Olivier Sarkozy's 8-Year RelationshipMary-Kate Olsen Officially Files for Divorce From Olivier SarkozyMary-Kate Olsen and Olivier Sarkozy Were at 'Different Places' in Life Before Divorce, Source Says