Picture this: An heiress is born four years before the death of her father. Her place in the succession should've been assured. That was before the new king's mother, Queen Mutemwiya, briefly took the helm as regent to the vast egyptian empire. Out of four known daughters born to the king (Tentamen, Amunipet, and another named Uiey") this Sitamen was not her daughter. In year 2, Mutemwiya embarked on a course that would alter egyptian history. Her son was now of age to take full control and needed a consort. But a babe of four years old would hardly do. Enter her niece, Tiye Nefertari. The rest would be history.
Sitamen is 6 years old as her brother, now 16, ascends the ancient throne of horus as sole ruler. Seven years later she may have heard whispers regarding her position. So why wasn't she married to her brother and given the rightful place her birth and rank demanded?

Ahmed Osman would have us believe that her place was usurped by Tiye. He'd also like you to believe that she did not consumate her "marriage" until year 23, at which time he states that she gave birth to Smenkhkare. She would've been twenty-seven years old then. If there is any truth to this, the date may be seen as the death-year of the crown prince, Thutmose. He would have been born around year 13. Perhaps with only one son left and pressure from the priesthood (who may have asserted her rights), Sitamen II was finally taken to pharaoh's bed.
But... Tiye was about 4 years younger then her husband, and could still hope for more sons. Surely she would've known that each child born to Sitamen only placed her own son(s) positons in deeper jeoprady.

The main question is: Did Thutmose IV have a daughter named Sitamen. The answer is yes. One of the titles that Osman uses for his Sitamen is: "Kings Daughter, Kings Sister, Kings Mother". To my knowledge, there are no inscriptions naming this Sitamen by those titles. Tiye's daughter is never referred to in those terms, even when her brother Akhenaten became pharaoh. She is always called Kings Daughter, Kings Great Wife. Of interest is the fact that she is referred to as a daughter of Tiye's, but not specifically of Amenhotep's. Of note, she is the only other wife (and he'd married two daughter's of his; Iset II & Henut'tanebu) specifically referred to in inscriptions and called "One who is Praised by the Good God". She also had her own distinct "lotus" crown and her own palace and estates. On the plan for Amenhotep's tomb, she is accorded burial. along with Tiye. Her chambers are somewhat larger then those of her supposed mother! There are also inscriptions on various articles of hers which have been tampered with, when regarding her birth and parents. Was there a coverup? Could there have been two Sitamen's?

Ahmed then goe's on to name Tutankhaten as another son of this union, born in year 34, eleven years later! This is with the understanding that a 10 year coregency was involved between Akhenaten & his father, and disregards his own "find" of an inscribed scarab in the temple of Osiris at Abydos. According to him, the inscription name's a "Meritre" as the mother of Tutankhamen. Since Tutankhamen always claims Amenhotep as his father and one of Tiye's daughters is named Meritre, do we find here the parents of Tut at last? If Osman is correct, then he makes an interesting connection with the boy-king's age. The date coincides with Tutankhamen's age at his accession. If he was born in year 34, he would've been 4 at his father's death, not counting the solo rule for Akhenaten (6) & Smenkhkare...(1?) He would have been ten at his coronation and between 18 - 19 at his death.

But what Osman doesn't take into consideration is one important factor; it is on record:
Sitamen was not recognised as the second "Great Wife" until year 30, eight years before Ammenhotep III's death. So it appears that this Sitamen couldn't be the daughter of Thutmose IV... or could she? Did Amenhotep III wait until she produced their second son before bestowing the honored title on her? And what need for a second "great royal wife" when the first was healthy and producing children? Did Tiye stop bearing heirs in year 30. Or better yet, did Akhenaten's inability to produce a male heir (after numerous atempts) have prompted Amenhotep to name two chief queens, so that either of the most direct heirs surviving would assure that dynasty's continuation? Such important questions may, to our great misfortune, never get answered.