[That’s what you get for believing a fourteen year old boy swinging a severed head around and making overbroad promises.]
It’s one thing to renege on poorly-armed and -prepared rabble and quite another to do so with respect to a courtier experienced in field maneuvers as as well as court intrigues.
https://en.m.wikipedia.org/w/index.php?title=Richard_II_of_England&diffonly=true#Downfall
[Henry had agreed to let Richard live after his abdication. This changed when it was revealed that the earls of Huntingdon, Kent, and Salisbury, and Lord Despenser, and possibly also the Earl of Rutland – all now demoted from the ranks they had been given by Richard – were planning to murder the new king and restore Richard in the Epiphany Rising.[108] Although averted, the plot highlighted the danger of allowing Richard to live. He is thought to have starved to death in captivity in Pontefract Castle on or around 14 February 1400, although there is some question over the date and manner of his death.[3] His body was taken south from Pontefract and displayed in St Paul’s Cathedral on 17 February before burial in King’s Langley Priory on 6 March.]