Supporting child through the death of an ex in-law?

I’m hoping for advice from others who have been in a similar situation.

Long story short, my ex-MIL was suddenly hospitalized and the prognosis isn’t good.

My son (6) doesn’t have much of a relationship with her (she is my ex husband’s mom). Ex-MIL saw my son a total of three times from birth-4 and then in the last six months has seen him maybe 3 or 4 more times. It was never clear to me why my ex-MIL didn’t want a relationship with my son, she was always simply “too busy” to spend time with him.

Not surprisingly, I do not have any respect for my ex-MIL. She treats everyone around her poorly and was particularly rude and condescending to me. It’s a situation where I’m very thankful that I haven’t had to deal with her since my ex and I split up.

All that said, I fully anticipate I will need to help him navigate the death of his grandma, regardless of how little she was around. I’m not sure what I say to him to comfort him when she never even prioritized a relationship with him. It’s doubly hard when she also treated me poorly for the ~15 years my ex husband and I were together.

I would love to hear from others who may have dealt with something similar. How do you help your kiddo feel better without lying about who that person was? I’d also love advice on navigating funeral attendance since I wouldn’t go if it was just me, but I would (of course) go to support my son.