Analysis of information sources in references of the Wikipedia article "Antony Armstrong-Jones, 1st Earl of Snowdon" in English language version.
...Margaret was the daughter of Sir Owen Roberts
Artist of 285 portraits
In 1899 Sir Robert Jones, who subsequently altered his name to Armstrong-Jones, had a son named Ronald. The family was, at that time, living in the London area and retained Plas Dinas as their country home in Wales. Sir Ronald Jones married Anne, and the marriage produced a son, Antony, who in 1961 [sic] married HRH Princess Margaret, the Queen's sister.