Complex sentence: The House of Chanel (Chanel S.A.) originated in 1909, when Gabrielle Chanel opened a millinery shop at 160 Boulevard Malesherbes, on the ground floor of the flat of socialite and textile businessman Étienne Balsan, as his mistress.
Split into simpler sentences: The House of Chanel (Chanel S.A.) originated in 1909, when Gabrielle Chanel opened a millinery shop at 160 Boulevard Malesherbes. She started on the ground floor below the flat of socialite and textile businessman Étienne Balsan, as his mistress.