Based on this passage about Ted Kennedy, at the time of his death, who were the three longest-serving senators of all time?

When Kennedy died in August 2009, he was the second-most senior member of the Senate (after President pro tempore Robert Byrd of West Virginia) and the third longest-serving senator of all time, behind Byrd and Strom Thurmond of South Carolina. Later that same year, he was passed by Daniel Inouye of Hawaii.[48] Kennedy therefore held the record as the longest-serving Democratic member of Congress to solely serve as a senator until October 2021, when he was surpassed by fellow Democrat Patrick Leahy of Vermont.

Based on this passage, Robert Byrd, Strom Thurmond and Kennedy were the three longest-serving senators of all time.