Polymerisation process for producing a heterophasic propylene copolymer, wherein said process comprises the steps of - polymerising propylene in a first slurry reactor, in the presence of a catalyst system comprising (i) a Ziegler-Natta procatalyst, (ii) an external donor and (iii) a cocatalyst, obtaining as slurry reactor product the first propylene homopolymer fraction of the polypropylene matrix - transferring the slurry reactor product into a 1 st gas phase reactor - producing the second propylene homopolymer fraction of the polypropylene matrix in the presence of the first propylene homopolymer fraction, obtaining as 1 st gas phase reactor product a mixture of the first propylene homopolymer fraction and the second propylene homopolymer fraction, - transferring said 1 st gas phase reactor product into a 2 nd gas phase reactor - producing the third propylene homopolymer fraction of the polypropylene matrix in the presence of said 1 st gas phase reactor product in said 2 nd gas phase reactor, obtaining as 2 nd gas phase reactor product a mixture of the first propylene homopolymer fraction, the second propylene homopolymer fraction and the third propylene homopolymer fraction, being the polypropylene matrix, - said first, second and third propylene homopolymer fractions, and having different MFR 2 (230°C) measured according to ISO 1133, - transferring the 2 nd gas phase reactor product into a 3 rd gas phase reactor - producing the elastomeric propylene copolymer in the presence of said 2 nd gas phase reactor product and at least one ethylene and/or C 4 to C 12 α-olefin, and - recovering the heterophasic propylene copolymer for further processing. - polymerising propylene in a first slurry reactor, in the presence of a catalyst system comprising (i) a Ziegler-Natta procatalyst, (ii) an external donor and (iii) a cocatalyst, obtaining as slurry reactor product the first propylene homopolymer fraction of the polypropylene matrix - transferring the slurry reactor product into a 1 st gas phase reactor - producing the second propylene homopolymer fraction of the polypropylene matrix in the presence of the first propylene homopolymer fraction, obtaining as 1 st gas phase reactor product a mixture of the first propylene homopolymer fraction and the second propylene homopolymer fraction, - transferring said 1 st gas phase reactor product into a 2 nd gas phase reactor - producing the third propylene homopolymer fraction of the polypropylene matrix in the presence of said 1 st gas phase reactor product in said 2 nd gas phase reactor, obtaining as 2 nd gas phase reactor product a mixture of the first propylene homopolymer fraction, the second propylene homopolymer fraction and the third propylene homopolymer fraction, being the polypropylene matrix, - said first, second and third propylene homopolymer fractions, and having different MFR 2 (230°C) measured according to ISO 1133, - transferring the 2 nd gas phase reactor product into a 3 rd gas phase reactor - producing the elastomeric propylene copolymer in the presence of said 2 nd gas phase reactor product and at least one ethylene and/or C 4 to C 12 α-olefin, and - recovering the heterophasic propylene copolymer for further processing.