And indeed, it will be [a cause of] regret upon the disbelievers. (69:50)

Almuntakhab Fi Tafsir Alquran Alkarim

And that it has distressed the minds of those who refuse to acknowledge Allah and are satisfied with the age of discord

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(69:50) and surely it will be a cause of regret for the unbelievers. *27

And indeed, it will be [a cause of] regret upon the disbelievers. meaning

*27) That is, they will ultimately have to despair and regret as to why they had rejected this Qur'an.
 

And indeed, it will be [a cause of] regret upon the disbelievers. meaning in Urdu

ایسے کافروں کے لیے یقیناً یہ موجب حسرت ہے