When Tristan and his wife divorced in 2005, Tristan obtained custody of his two sons, Dean and Matt. At the time of the divorce, Dean was turning 16 and Matt was turning 12. Both sons lived with Tristan in the family home. Tristan was permitted to retain ownership of the house as part of the divorce settlement agreement with his wife. From on or around 2006, Tristan would often share information with his sons about the financial circumstances that the family was in at that time. There were multiple conversations and a recurrent theme of the conversations, particularly to Dean, were words to the effect of: "I am struggling to pay the mortgage" "I couldn't pay all the bills this month" "If you don't want to work and help me with the mortgage, we might as well sell the house because I can't afford it by myself" During the period of 2007-2009, Tristan would continue to regularly say to his sons that he may need to sell the house and that as a result they may all have to move into an apartment as he could not afford the mortgage. Tristan would say to Dean words to the effect of: "If you help me with the mortgage repayments, I will make sure that you will be taken care of" "I don't want to have to sell this house. I want this house to become yours and your brother's one day, but you need to help me" "You are lucky I was able to pay for your private school education and not to mention, all those holidays we had!" Dean took Tristan's comments to mean that Dean will one day obtain an interest in the house if he would help Tristan with the mortgage repayments. Dean enrolled in an accounting course in 2008 and he started working part-time for an accounting firm during the academic year and full time when he was on university holidays. He deposited half of what he earned from 2008-2012 into Tristan's bank account (approximately $20,000 for the four-year period). After graduating in 2012, he obtained a full-time job, but because of other financial commitments, he reduced the regular payments to Tristan's bank 4 of 4 account (depositing approximately $100,000 for the period between 2012-2022). From 2009 onwards, Tristan made fewer comments about struggling to pay the bills and the mortgage. Last year, Dean stopped making the regular payments when he moved out of the house due to not approving of Tristan's new girlfriend, who has since moved into the house. During the time that Dean and his brother were living with Tristan, neither Dean nor Matt paid rent, utility bills or contributed towards day-to-day expenses such as groceries. They could use Tristan's car and boat, and they would often have holidays together that were fully paid for by Tristan. Unlike Dean, Matt had never contributed to the mortgage repayments, but he would often make improvements to the house and continues to live in the house with Tristan. Tristan is now thinking of selling the house as he is keen to downsize and go overseas with his new girlfriend. The house has been valued at $750,000. Tristan is claiming that he is the sole owner of the house. Dean has come to you for advice as to whether he can rely on equitable estoppel to enforce his father's promise to him in relation to the house and what would be his likely remedies.

Discuss proprietary estoppel or the relevant estoppel with australian law.