Albert Barnes Commentary Daniel 5:10

"[Now] the queen by reason of the words of the king and his lords came into the banquet house: the queen spake and said, O king, live forever; let not thy thoughts trouble thee, nor let thy countenance be changed." — Daniel 5:10 (ASV)

Now the queen - “Probably the queen-mother, the Nitocris of Herodotus, as the king’s wives were at the entertainment.” - Wintle. . So Professor Stuart.

The editor of the “Pictorial Bible” also supposes that this was the queen-mother and thinks that this circumstance will explain her familiarity with the occurrences in the reign of Nebuchadnezzar. He says, “We are informed above, that the ‘wives and concubines’ of the king were present at the banquet. It therefore seems probable that the ‘queen’ who now first appears was the queen-mother; and this probability is strengthened by the intimate acquaintance which she exhibits with the affairs of Nebuchadnezzar's reign. During the latter part of his reign, she, as the wife of Evil-Merodach (who was regent during his father’s mental derangement), took an active part in the internal policy of the kingdom and in the completion of the great works that Nebuchadnezzar had begun in Babylon. This she continued during the reigns of her husband and son, the present king Belshazzar. This famous queen, Nitocris, therefore, could not but be well acquainted with the character and services of Daniel.”

On the place and influence of the queen-mother in Oriental courts, see Taylor’s Fragments to Calmet’s Dictionary, No. 16. From the extracts Taylor has collected, it would seem that she held an exalted place at court, and that it is entirely probable she would be called in, or would come in, on such an occasion. See also Knolles’ “History of the Turks,” as quoted by Taylor, “Fragments,” No. 50.

By reason of the words of the king and his lords - This refers to their words of amazement and astonishment. These words would doubtless be conveyed to her, as there was so much alarm in the palace and a summons to bring in the wise men of Babylon.

If her residence was in some part of the palace itself, it would be very natural for her to be made acquainted with the unusual occurrence. Or, if her residence was, as Taylor supposes, detached from the palace, it is entirely probable that she would be informed of the prevailing consternation. Recollecting the case of Nebuchadnezzar and the forgotten services of Daniel, she would then realize that the information sought about the mysterious writing could be obtained from him.

And the queen spake and said, O king, live for ever - This is a common salutation when addressing a king, expressing a desire for his happiness and prosperity.

Let not thy thoughts trouble thee ... - That is, there is a way by which the mystery may be solved, and you need not, therefore, be alarmed.