To say something suddenly and without thinking, usually because you are excited or nervous. (Cambridge Dictionary)
To utter abruptly and impulsively —usually used with out. (Merriam -Webster)
If someone blurts something, they say it suddenly, after trying hard to keep quiet or to keep it secret. (Collins Dictionary)
To utter suddenly or inadvertently; divulge impulsively or unadvisedly (usually followed by out): (Dictionary.com)
Say (something) suddenly and without careful consideration. (Oxford Dictionaries)
“I’m sorry you died,” I blurt out, meaning it.
Blurt out. Thesaurus. plus.