Paul McCartney has issued a tribute to Beatles producer George Martin, hailing his influence on the group and saying that he thought of him as a “second father.”

McCartney posted an appreciation on his PaulMcCartney.com website on Wednesday for the esteemed producer who died Tuesday at the age of 90. Martin worked as a producer and arranger for McCartney several times in the post-Beatles era, notably on his soaring James Bond theme “Live and Let Die.”

“He was a true gentleman and like a second father to me. He guided the career of the Beatles with such skill and good humour that he became a true friend to me and my family. If anyone earned the title of the fifth Beatle it was George,” McCartney wrote. “From the day that he gave the Beatles our first recording contract, to the last time I saw him, he was the most generous, intelligent and musical person I’ve ever had the pleasure to know. …. The world has lost a truly great man who left an indelible mark on my soul and the history of British music.”

McCartney recalled Martin’s role in persuading him to use a string quartet on the song that was destined to become one of the Beatles’ signature tunes, “Yesterday.” At first McCartney resisted the idea, given the Beatles’ rock ‘n’ roll roots.

“With the gentle bedside manner of a great producer he said to me, ‘Let us try it and if it doesn’t work we won’t use it and we’ll go with your solo version.’ “McCartney wrote. “He took my chords that I showed him and spread the notes out across the piano, putting the cello in the low octave and the first violin in a high octave and gave me my first lesson in how strings were voiced for a quartet. When we recorded the string quartet at Abbey Road, it was so thrilling to know his idea was so correct that I went round telling people about it for weeks.”

Abbey Road Studios, the EMI facility where the Beatles and Martin made musical history starting in 1962 through the band’s 1969 swan-song album “Abbey Road,” also paid tribute to Martin.

“Sir George transformed music recording with his creative flair, innovation and passion and we want to express our deep sadness at losing such an immensely talented, charming and warm man,” the org said in a statement. “We are committed to ensuring Sir George’s visionary legacy lives forever at Abbey Road Studios, and we are hugely honored to be part of his story.”