yoko ono said she was ` very saddened ' by news of cynthia lennon 's death .
she praised cynthia , 75 , as a ` great person ' with a ` strong zest for life '
cynthia lennon , nee powell , married john lennon after they met at college .
she is the mother of the musician 's son julian lennon , who is now aged 51 .
but the couple divorced in 1968 after lennon left her for artist yoko ono .