Who is Secretariats Siblilings?

Although Christopher Chenery was recorded as the official breeder of Secretariat, well-known racing columnist Bill Nack wrote in his book on the racehorse that Penny Chenery made the decision to breed their mare Somethingroyal to Bold Ruler twice. The first mating in 1968 produced the filly The Bride. The second breeding, in 1969, resulted in Secretariat. There is no other siblings listed.