Retired maths teacher John Rowley admits his 18,000-piece jigsaw is "a bit of a challenge," after spending around 1,000 hours piecing it together.
It is a slow and painstaking process assembling the jigsaw
Mr Rowley, 63, from Acrefair near Wrexham, has a lifelong passion for puzzles, and this monster takes up almost the length of his living room.
Measuring 3.21m x 1.56m (10ft 6ins x 5ft 1in) it could be the world's largest commercially available jigsaw.
He spent an average eight hours a day working on an old master's painting.
The St Columba Altarpiece was painted by Rogier van der Weyden in 1455.
"You can't get a bigger one," said Mr Rowley minutes before he clipped the last piece into place.
"As you get near the end, you're counting the gaps and the number of pieces you've got. You don't want to find any have gone missing".
"It's a bit of a passion," he said.
"Since I was about 20, I've always completed large jigsaws - 4,000, 5,000, even 7,000 pieces. Last winter I decided to find the largest and tackle it.
"It's a wonderful thing to do over the winter. It really keeps me occupied and I'm over the moon with it".
His other interests - the Rubik's Cube and Soduku puzzles - take up much less space.
"It takes a lot of handling to organise it well.
"I'm like everybody else. You sort them out and you start with the outside.
"An outside piece gives you a colour that leads off it and you gather those colours and build on that section".
Mr Rowley has worked for up to 11 hours a day on the puzzle
The puzzle was made by the Spanish company Educa, which manufactures the world's biggest commercially available jigsaws.
The first jigsaw has been credited to the 18th Century British mapmaker John Spilsbury.
Mr Rowley has organised completed sections onto sheets of A4 paper to save space. The sections can be quickly clipped together to build the completed work.
Ultimately he hopes his labour of love could be framed and put on display.
"I'd love it go somewhere where people can actually see it. It's a religious painting and a church or church hall would be ideal," he said.