In 1619 his daughter died shortly after birth, the only child he was to have. In 1620 after the execution of his father he began to call himself the Baron of Muiresk, which in Scotland was considered an illegitimate claim. His brother James, though disinherited from the estate, still had a claim to the title, which was considered to end with his death, as he had no heir. In any case Thomas was not the second son but the third. The second (Robert) had no heirs, either, which did not strengthen the case of the Dempsters. They were forced to accept the end of their clan; that is, there were no further charters to Dempsters from the king, nor was anyone entitled to be called Baron Dempster or use the coat of arms. Modern Dempsters, of course, may do as they please in accordance with the laws of the countries in which they reside.