I loved the books as well! I also loved the original French series which was televised in the early Seventies. Haven't seen the new film...
If I remember rightly, in the Druon version Mahaut didn't
succeed in murdering the infant Jean I - he had been substituted for the son of his wet nurse, and appears in later books as a grown up. It is the wet nurse's son who is poisoned by the countess at the christening when she puts her finger dipped in poison in her mouth!
A lot of events (like the above) are pure speculation. Druon also has Robert of Artois responsible for the poisoning of Mahaut and her daughter much later on. However it is well researched speculation, so it is an plausible embellishment of historical facts. Maurice Druon is, I believe, still alive and is the sometimes controversial head of the Academie Francaise. It's certainly likely that Mahaut would be keen to have her son in law on the throne, as this helped her shortly afterward in the second of the three court cases in which she successfully defended her claim to Artois.
Interestingly her claim to Artois (where a daughter has precedence over a deceased son's children) was quite the opposite of the male line succession which was behind Philippe V and Philippe VI's claims. It was ironically more like Edward III's female line claim to the throne of France, which was supported by Mahaut's nephew and enemy, Robert of Artois. As she was the only woman on the council of peers of the realm, representing both the County of Burgundy and Artois, she would have been pretty tough, I imagine.
It is probable that Nogaret died in 1313 (though dates in the fourteenth century are notoriously unreliable), which makes casts doubt on Druon's account in "The Iron King", where Nogaret is summoned by the Grand Templar at the stake to appear with the King and the Pope before the throne of God within a year.
We had good fun on the Tudor forum discussing the question of whether Queen Isabella was responsible for the downfall of her sisters in law (also in "The Iron King").
Which of the books did you like best?