I’m glad somebody mentioned that.
I’ve never heard that before. A quick google finds no support for it. It sounds like an urban back-formation.
You can also sing either to* “Stairway to Heaven”*. Gilligan’s song becomes terribly plaintive when taken up the stairway.
I knew it first as “What Child is This”, and still don’t know the (real) lyrics to “Greensleeves”, but I know that the latter far preceded the former. I’d be interested in knowing where the various respondants are from: It’s my understanding that most Americans know it first as “What Child is This”, but that most non-American Anglophones know it first as “Greensleeves”. I’m an American (Ohioan, to be more specific).
Alas, my love, you’ve done me hurt
You’ve sewn green sleeves on my purple shirt
And, what’s worst of all
You went and made me wear it
Never, ever heard of this dubious ‘carol’.
Next up: ‘The Lincolnshire Poacher’ as a papal hymn in the Sistine Chapel when the white smoke goes up.
“Oooooooooooooooooooooooooooooooooooooooooooooooohhhhhhhhhhhhhhhhh, 'Tis my Delight on a Shining Night, in the Season of the Year”.
<snipped for brevity>
Genius! And it perfectly fits my image of something Henry VIII might actually sing about.
I reckon that might have been the first draft. 
On the thread’s general theme: there comes to my mind, something from 45-odd years ago. In the UK (where, per my impression, the “Greensleeves” song / tune is basically a secular thing – we don’t noticeably have the “What Child” carol) – back then, there was a big commercial-type scene run by the prominent supermarkets, involving “Green Shield stamps”; small numbers of which were issued to customers with their purchases: the customer stuck said stamps into the book for them, with which customers were provided – when the book was full, customer submitted it, and could get various discounts / reductions on assorted goods.
A fellow-student of mine at university then, made up what I considered quite a clever “Greensleeves” parody. Ditty thus thought up by this girl, was the woeful plaint of a guy unrequitedly in love with a young lady who worked as a supermarket cashier – whereby the fellow bought at that supermarket, huge amounts of groceries (far more than he needed) in the never-realised hope of getting something going with the object of his hopeless passion. The refrain was:
“Green stamps were all she gave,
Green stamps were all I took;
Green stamps only for me, her slave,
And I pasted them all in my green-stamp book.”
Am I the only thing who’s filked WCIT?
What child is this/That on me has pissed/When I changed his diapers on Christmas Day?
Ah well.
American, raised in a non-religious household, Ren Faire worker, didn’t even know about the Xmas version until a few years ago.!
I’m getting old. Filk?
Filk is a range of music found in Science Fiction/Fantasy conventions. It started off as SF-themed parodies of famous folk songs, and then developed into original songs, many on themes that aren’t even SF or Fantasy related (cats, for instance). The term came about due to an early misprint of the word “folk” which stuck.
On his Christmas album, Mason Williams has a track titled “What Tune Is This?” which blends Greensleeves (which he charted with) with his other, better known hit Classical Gas.
Thank you. I did try to keep a kind of Early Modern sensibility to the wordplay, mixed with some classic Mid-Twentieth Century Novelty Record stylings.
I learned it as “Greensleeves” when I was a kid. I was at least in my 20s when I first heard the Xmas version.
Just as “Ding Dong Merrily on High” is that carol to the tune of the “Branle de l’Official.” 
“Gilligan’s Island”
“Ode to Joy”
“Amazing Grace”
“House of the Rising Sun”
“Yellow Rose of Texas”
“Clementine”
and the list goes on and on…
I like to sing “The Marines’ Hymn” to the tune of “I’d Like to Teach the World to Sing”
What’s really annoying, is for a long time there, I had “The Wreck of the Edmund Fitzgerald” stuck in my head… except to the tune of “Stairway to Heaven” (both of those also being on that long list of songs).
The words came from a poem written by William Chatterton Dix, an Englishman. They were later set to the old tune. Apparently “What Child Is This” is more popular in the US, despite its roots.
How many people knew that Cat Stevens’s hit “Morning Has Broken” was originally a Christmas carol called Child in a Manger?
*Blackbird has spoken, like the first bird.
*
Well, Morning has Broken as a christian hymn was written in the 1930s ( by Eleanor Farjeon, who was once famous ), and is still sung by Mixed Infants in School Assembly; it shared the old Scottish tune, Bunessan with that carol.
Sweet the rain’s new fall, sunlight from heaven.
Despite that, I still object to the mingling of the Sacred and the Profane. The Profane usually gets the short end of the stick.
Mine is the sunlight, mine is the morning.
I grew up singing “Morning Has Broken” in church, in the grown-up hymnal, with Eleanor Farjeon
listed as the author.
What makes it “dubious”?
At least in the US, it is one of the most popular overtly religious Christmas songs.
Dubious because religious stuff shouldn’t be tacked on to traditional secular stuff. * They already have so much, can’t they leave the rest alone ?
We here don’t admire Henry VIII for much of his life’s work, but most of us admit the man could carry a tune. Imagine in the future some pastor latching on to* Jimmy Shagdog and the Shaggers*’ 1983 Disco masterpiece ‘Shag Me All Night Long’, and altering it to convey God’s Glory,: ‘Praise Him All Night Long’;
*
“What Jimmy meant to say here, ‘Oh baby ! Fucketty Fucketty Doo, Don’t Stop Now’ is that we must persevere.”*
- Nor is taking religious stuff like chalices and stained glass ( and bodies ) and putting them in secular museums particularly acceptable. Render unto Caesar….