Sir George Martin, the record producer known as the "Fifth Beatle", has died aged 90, Ringo Starr has said on Twitter.
Sir George helped the Beatles achieve global success as the head of the Parlophone record label after hearing their demo tape in 1962.
Starr, 75, tweeted: "God bless George Martin peace and love to Judy and his family love Ringo and Barbara. George will be missed."
He captioned a picture of the Fab Four and Sir George with the phrase: "Thank you for all your love and kindness George peace and love."
Sean Ono Lennon, son of John and Yoko, posted a picture of Sir George on Instagram with the caption: "R.I.P. George Martin. I'm so gutted I don't have many words. Thinking of Judy and Giles and family. Love Always, Sean."
Beatle Ringo Starr wrote on Twitter: "God bless George Martin peace and love to Judy and his family love Ringo and Barbara. George will be missed."
Alongside a picture of Sir George with the Fab Four he added: "Thank you for all your love and kindness George peace and love."
Singer Lenny Kravitz wrote on Twitter: "The legends are really going home! Visionary producer of TheBeatles, George Martin (1926-2016)."
Liam Gallagher wrote simply: "Sir George Martin RIP LG x"
Singer Josh Groban said: "Every time I record at abbey road I geek out and play with the mics sir George Martin used. What an ear, what a life, what a legacy."
Television presenter Piers Morgan said: "RIP Sir George Martin. The 5th Beatle, producer extraordinaire & a musical genius."
UK Prime Minister David Cameron also paid tribute online, writing: "Sir George Martin was a giant of music - working with the Fab Four to create the world's most enduring pop music."