The 82-year-old Japanese star praised the late artist, who died at her home in Spain earlier today (01.04.15), for being a ''wonderful mother'' to her and the Beatles star's 51-year-old son Julian Lennon.
In a statement, the singer and activist said: ''I'm very saddened by Cynthia's death. She was a great person and a wonderful mother to Julian.
''She had such a strong zest for life and I felt proud how we two women stood firm in the Beatles family. Please join me in sending love and support to Julian at this very sad time.''
John and Cynthia separated in 1968 after he left her for Yoko, whom he was married to until his death in 1980.
Former Beatles star Paul, 72, also posted a touching message about Cynthia on his website, writing: ''The news of Cynthia's passing is very sad. She was a lovely lady who I've known since our early days together in Liverpool. She was a good mother to Julian and will be missed by us all, but I will always have great memories of our times together.''
His bandmate Ringo Starr, 74, sent his best to Julian via Twitter, writing: ''Peace and love to Julian Lennon. God bless Cynthia love Ringo and Barbara xx.''
Julian's team announced the sad news via a post on his website earlier today, which read: ''Cynthia Lennon passed away today at her home in Mallorca, Spain following a short but brave battle with cancer.
''Her son Julian Lennon was at her bedside throughout. The family are thankful for your prayers.''