[Yoko] told me that it was my job to “keep John happy” by buying whatever he asked me to get and by generally keeping him company when he was lonely or bored. If he made any unusual requests or behaved strangely, I was to bring it to her attention. She also warned me that all kinds of people would try to contact John, and she made it very clear that I was never to put anybody through to him without her permission. She specifically cautioned me about taking calls from John’s teenage son, Julian, or the boy’s mother, Cynthia, as well as from Paul McCartney and the other ex-Beatles. (...) The next day, George Harrison called the Dakota and left a message for John. Winnie, the concierge, handed me a piece of paper on which she had written: “PLEASE CALL GEORGE – HE’S VERY ANXIOUS TO TALK TO YOU AFTER AN ABSENCE OF TEN YEARS!” When I gave John the message, he was less than thrilled. “Well, it’s kind of George to call after forgetting to mention me in his book,” he snickered. He gave me back the note and told me to “let Mother deal with it.” (...) Also around this time, there was a message from Paul McCartney wishing John luck [with the Double Fantasy sessions]. When I told Yoko that Paul had called, she looked alarmed. “You better not tell John,” she said, worrying that Paul would want to get in on the session.
John Lennon: Living on Borrowed Time, Frederic Seaman (1991)