that was Tambora in 1815. The ‘little ice age’ ended a few years before and then ‘BAM’.
https://en.wikipedia.org/wiki/1815_eruption_of_Mount_Tambora
(yes it is wikipedia, but, it’s good for this context. I was a librarian before retirement and it is a good source for general consumption)
The more recent Mt. Pinatubo eruption that closed down our military base in the Philippines also probably caused slightly lower temperatures the following summer (like 1 degree).