I think it is kind of strange that Shiv knew Mahen's plan from the start. Because if you look way back to the start of how he treated her, how he point blank refused to marry her, refused to accept her as his wife and how he treated her like dirt. If all he ever wanted was the land then wouldnt he have been nicer. Gauri refused to listen to Devika because she is so emotional, but shiv is more practical. Devika calls up Shiv and tells him everything and about shashank. That is why shiv said 'this has been planned way before' because Devika was bitter towards Mahen from the start so she must have told him how his father was manipulating Alok from the start. Remember Shiv did not know that Mahen had invested so much money on a rival property land so this cannot have been Shiv's plan from the start. I think Shiv found out from Devika, Devika told him Shashank's back, he goes to meet shashank and tells him to get back to Gauri so that to stop his father and his evil plans. He even offers shashank that he would leave, because if shiv is still in the picture. Gauri would not leave him and Mahen would continue blackmail Shiv about disowning him and Palak.