She bought him his first guitar and cheered him on when The Beatles became successful. Louise even entertained some of George’s most avid fans in her home and had a five-year-long correspondence with one.
So, it’s only natural that George was beside himself when she became ill in 1970. And when a musician’s emotions run high, no matter what they are, we all know what happens: they write songs.
In his 1980 memoir, I Me Mine, George wrote that “Deep Blue” came to him when his mother was very ill and dying.
“I wrote ‘Deep Blue’ during the making of the All Things Must Pass LP,” George wrote. “It’s a bit obscure as it was only the ‘B-side’ of the ‘Bangla Desh’ single and never appeared on any album.
“It was written during the year my mother was very ill, and dying, and after going in the hospitals over and over again; it’s that smell and the whole atmosphere of doom that’s in those hospitals.
Source: cheatsheet.com