John 6:8

λέγει αὐτῷ εἷς ἐκ τῶν μαθητῶν αὐτοῦ, Ἀνδρέας ὁ ἀδελφὸς Σίμωνος Πέτρου·

Rough Word-by-word:
he says to him one from the disciples of him, Andrew the brother of Simon Peter,

Smooth Translation:
One of his disciples, Andrew, the brother of Simon Peter, said to him,

Notes:
Interesting grammar...The genitive prepositional phrase is modified by the numeral in the nominative, making it a substantive adjectival clause in apposition with the proper noun, Andrew, which is in apposition with the nominative clause which includes the two proper nouns, Simon Peter, which are also in apposition with each other.

The genitive prepositional phrase acts like a nominative and is in fact modified by the nominative adjective, εἷς. I think this might be what is called a genitive absolute.

λέγει verb present active indicative 3rd singular from λέγω (I say) "he says"

αὐτῷ pronoun dative singular masculine "to him"

εἷς numeral nominative singular masculine "one" (note the rough breathing)

ἐκ genitive preposition "from, out of"

τῶν definite article genitive plural masculine "the"

μαθητῶν noun genitive plural masculine "disciples"

αὐτοῦ pronoun genitive singular masculine "of him"

Ἀνδρέας proper noun nominative singular masculine "Andrew"

ὁ definite article nominative singular masculine "the"

ἀδελφὸς noun nominative singular masculine "brother"

Σίμωνος proper noun genitive singular masculine "Simon"

Πέτρου proper noun genitive singular masculine "Peter"