After the fall of Harlech Castle in February 1409, various members of Owain Glyndwr’s family were taken to the Tower. Among them was his grandson, Lionel ap Edmund (or Lionel Mortimer) the young son of Sir Edmund Mortimer and his wife Catrin ferch Owain. This boy cannot have been older than six at the uttermost, and may well have been considerably younger, perhaps even a babe in arms.
Lionel was (theoretically) heir to the earldom of March after the young Earl of March and his brother, and thus very close in blood to the Mortimer claim to the English throne. In addition, he was descended from all the principal Welsh princely houses, including that of Gwynedd. (Ironically through his father, who descended from Gwladys Ddu, daughter of Llywelyn ap Iorwerth.)
In 1413, Catrin Mortimer and two of her daughters were buried in St. Swithin’s Church in London. The fact the three of them were buried together suggests death by contagion of some kind, although this is only a probability. However, what happened to Lionel and his remaining sister is unknown. Apparently they went into the Tower and never emerged.
Nevertheless, as far as I know, no one has ever accused Henry IV or Henry V of murdering them.
Catrin’s mother apparently outlived her, but we don’t know what happened to her either. The Tower has many secrets, but some of them appear to provoke very little curiosity.