A corner element for a right-angled outer corner (OC), characterized in that the corner element comprises a first edge strip and a second edge strip , wherein said first and second edge strips are configured to be attached to a wall structure (W1, W2, OC) for the mounting of a wall board (B, B1, B2, Bn, B(n+1)) against the wall structure (W1, W2, OC), the first and second edge strips each being composed of an elongated element suitable for length adaption through cutting in a length dimension (L) to an extension of the wall structure (W1, W2, OC) in a specific dimension, the first and second edge strips each comprising: a connection part (A1) arranged in a first side extending in the length dimension (L) and is configured to be connected to a connection means integrated into the wall board (B, B1, B2, Bn, B(n+1)), which connection means extends along a first side of the wall board (B, B1, B2, Bn, B(n+1)), such that the wall board (B, B1, B2, Bn, B(n+1)) is attached to the wall structure (W1, W2, OC), the connection part (A1) comprising click-in means (111, 112, G) configured to receive the connection means of the wall board (B, B1, B2, Bn, B(n+1)) and interconnect the wall board (B, B1, B2, Bn, B(n+1)) and the respective first and second edge strip , such that the wall board (B, B1, B2, Bn, B(n+1)) becomes attached to the wall structure (W1, W2, OC), and an adaption part (A2) arranged in a second side opposite to the first side , which adaption part (A2) extends in the length dimension (L), wherein the first and second edge strips each comprises a third side and a fourth side both extending in the length dimension (L) and being mutually opposite to one another, and wherein the adaption part (A2) consists of a flat side surface showing a first angle (α1) of 45 degrees towards the third side and a second angle (α2) of 135 degrees towards the fourth side , wherein said adaption part (A2) of said first edge strip is configured to be attached on a primary side (S1) of a right-angled outer corner (OC) in the wall structure and there cooperate with the adaption part (A2) of the second edge strip being attached on a secondary side (S2) of the right-angled outer corner (OC) such that the edge strips by contacting between the respective adaption parts (A2) together form the corner element starting from which wall boards may be attached to the wall structure (OC) along the primary side (S1) and the secondary side (S2) respectively, and wherein the adaption part's (A2) flat surface in the first and second edge strip respectively is configured to receive a joining plate for fixating the first edge strip relative to the second edge strip . a connection part (A1) arranged in a first side extending in the length dimension (L) and is configured to be connected to a connection means integrated into the wall board (B, B1, B2, Bn, B(n+1)), which connection means extends along a first side of the wall board (B, B1, B2, Bn, B(n+1)), such that the wall board (B, B1, B2, Bn, B(n+1)) is attached to the wall structure (W1, W2, OC), the connection part (A1) comprising click-in means (111, 112, G) configured to receive the connection means of the wall board (B, B1, B2, Bn, B(n+1)) and interconnect the wall board (B, B1, B2, Bn, B(n+1)) and the respective first and second edge strip , such that the wall board (B, B1, B2, Bn, B(n+1)) becomes attached to the wall structure (W1, W2, OC), and an adaption part (A2) arranged in a second side opposite to the first side , which adaption part (A2) extends in the length dimension (L), <EOS>