Foaled in Great Britain in 1853, Bonnie Scotland came to Belle Meade Mansion in Nashville, Tennessee, in 1872, at the age of 19. Even though he died at Belle Meade in February 1880, he was named the outstanding sire of that year. Here is a short listing of some of the pedigreed horses from his line: Bramble, 1875, earned $32,660; Man-O-War, 1917, earned $249,465; Prince Rose, 1928, earned $59,267; Sea Biscuit, 1933, earned $437,730; War Admiral 1934, earned $273,240; Secretariat, 1970, earned $1,316,808; Seattle Slew, 1974, earned $1,208,726; and Affirmed, 1975, earned $2,393,818.
https://www.crossville-chronicle.com/news/local_news/pedigree-of-derby-winners/article_9dbd72f6-10e1-5335-a8e0-58e718b40bda.html
Point is as you go down the years the horses ancestors grow exponentially. So chances are the great horses of the past are going to be in the background of current stars.
This is definitely true when you expand beyond the silly obsession with tail-male (“all THs descend from 3 stallions”)and see how so many horses contribute to one horse now. Sometimes multiple times (inbreeding, or linebreeding).