Willem Knap was the youngest of three children of Simon Knap and Hendrika Wolffers. At the time that he was registered at the Jewish Council of Amsterdam, he was listed as "unmarried". However, Willem is still in the summer of 1942, before he was deported to Auschwitz married in Rotterdam to Grietje Frenk a daughter of Aron Frenk and Elisabeth Velleman.
On Willem's record of the Jewish Council it is to read that he has arrived in transit camp Westerbork on 31 July 1942 and deported to Auschwitz on 3 August 1942. Whether his wife Grietje Frenk also was deported on that same 3 August to Auschwitz is not clear: her record from the Jewish Council does not mention anything like that. But both have been kille in Auschwitz on 30 September 1942.
City Archive of Rotterdam, family registration card of Simon Knap; file cabinet of the Jewish Council of Amsterdam, record of Willem Knap and Grietje Frenk and an addition of a visitor of the website.