This part of the verse is an 'aside'; it is a "look-ahead" reference to events ( ~70 A.D. ) that do not even take place within the 70 weeks, and has absolutely no connection what-so-ever with the "counting" of weeks or the events that are associated with those weeks.
'Look ahead...events (70 A.D.) that do not...take place within the 70...no connection what-so-ever with the...counting...of weeks or the events that are...with those week'----------YES. That IS absolutely the point. The nail on the head: That is a break in the 70 weeks. Specifically, and Only (and grammatically, numerically, countingly, textually, plainly, prophetically)
a break between the end of the 69th seven and the 70th seven. Which, as of now, stands at about 1,985 years (AD 30 to present).
There is no reference to the word 'prince' ( in verse 26 ) anywhere in the passage. All three of the words 'he' in verse 27 refer back to the word 'Messiah' in verse 26.
This plainly contradicts not only English (the translation), but the manner All language in literature and in speaking works.
I means it's so........silly, especially baldly stated as it is, with no proffer of a reason even attempted...
The Messiah is mentioned first in 9:26. His crucifixion. Marking the end of the 62 sevens (434 years)---which also happens to be the end of the (7+62=69) sevens (483 years), since the 7 sevens came BEFORE the 62 sevens.
After the word 'Messiah' appears, who 'will have nothing' (= nothing of worldly success, having been executed as a criminal by the Romans for the Jews, His own people), the 'prince who will come [and] destroy [Jerusalem] and the [temple]' is mentioned. Plainly not Messiah. Not Jesus. But, in fact, rather (as the earlier poster Correctly identifies) came and destroyed
Jerusalem and its temple in AD 70. Titus the Roman general. A relief of his victory and the spoils like the lampstand from Jerusalem's temple in AD 70, still stands in Rome. The Lord Jesus prophesied of Titus' war in Matthew 24:2, among other places. Since they rejected their true Messiah, in favor of their own continuing religious and political clout (as pathetic as it was), God gave them up to following all kinds of self-declared 'Christs' and zealots and revolutionaries, such as Bar-Kochba, I believe, is one. Leading to Rome being fed up and destroying the nation 40 years after it 'destroyed' Jesus. (Actually, this was in Jesus' plan: to accomplish redemption both for them, and Romans, and for the entire planet of people; and to fall into the earth as a grain of wheat and die... It is so fitting that Daniel be a rare ---only?---OT book to explicitly teach the term 'resurrection' (in chapter 12)).
But back to the grammar-point: the antecedent (the precedent, the precursor) of the pronoun 'he' in Daniel 9:27 is the last-mentioned person-noun. The 'prince of the people who will come.' Titus, the Roman prince of the Roman empire, in AD 70.
Not Jesus Christ. This is confirmed (as if such 'needed' confirmation), by the description of what the 'he' does in Daniel 9:27 which Jesus did not do directly and physically; and even more: Jesus Christ is the OPPOSITE of the desolator with the desolator's abomination of desolation. (Of which the Lord also prophesied....in relation to Daniel 9:27...which had of course not yet transpired at Jesus Christ's time----the abomination of desolation spoken of through Daniel the prophet, in Matthew 24:15.)