Kelly Rizzo fell head-over-heels for her late-husband Bob Saget ... but it wasn't love at first sight -- she says she initially hated the fact he slid into her DMs.

The TV host told Jack Osbourne how they got together on his "Trying Not To Die" podcast ... she explained, "He saw me on Raya, but I didn't see him." Getty

Evidently, Bob figured since Kelly was a Chicago media personality, his friend in Chicago radio might know her. His hunch was correct, and his friend reached out to Kelly, letting her know Bob was going to DM her.

Kelly recalled, "I was like, 'Ew... why?' I was not interested at first."

She noted Bob was 23 years older than her and not really her type. But his messages were so nice, she thought maybe they could be friends.

Jack asked, "You friend-zoned him r

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