What is the evidence that Thomas Aquinas was assassinated?

Reading the Wikipedia article on [Thomas Aquinas](https://en.wikipedia.org/wiki/Thomas_Aquinas) , I stumbled on something rather peculiar. Apparently he fell ill and died at the age of 49 on his way to the [Second Council of Lyon](https://en.wikipedia.org/wiki/Second_Council_of_Lyon) , where he had been summoned by the pope to participate in an effort to reunite the Western and Eastern churches. Maybe I'm a bit jaded, but it seemed fishy to me that a preeminent scholar "just so happened" to die on his way to such an important event. I was thus pleased to note that the great [Dante](https://en.wikipedia.org/wiki/Dante_Alighieri) had similar misgivings: he wrote in the [*Divine Comedy*](https://en.wikipedia.org/wiki/Divine_Comedy) that: > Charles came to Italy, and for amends / A victim made of Conradin, and then / Thrust Thomas back to heaven, for amends. ([*Purgatorio*, 20.67–69](http://www.divinecomedy.org/divine_comedy.php3?display?Enface?Purgatorio?20???151?1???0??1?1)) "Charles" here is apparently [Charles I of Naples](https://en.wikipedia.org/wiki/Charles_I_of_Naples) . Wikipedia cites a historian who disputes Dante's speculations, but I'm not giving up so easily. What is the evidence, if any, that Aquinas was assassinated?