ricordare is reflexive in Italian, so
qualcuno si ricorderà (someone will remember). But there is a direct object, the target of remembering: qualcuno si lo ricorderà as the direct object is closest to the verb. However doubled up si becomes se so
qualcuno se lo ricorderà. Tricky.
PS se means if which also helps ....
Great explanation Peter. To extend this idea, here is a chart that shows how the pronouns change when they are doubled up like 'se lo'
Si ricordare - to remember - is reflexive. The si means "one[self]". However, when the pronoun si stands before another pronoun the i will change into an e, i.e. se. Like in this sentence, Se lo ricorderà.
I hope you understand what I'm trying to say. My mother tongue is Swedish and explaining grammatical stuff in English isn't exactly my specialty.