"Everyone buys into the same goal," said the former Leicester scrum-half, who retired with knee problems a year after returning from South Africa.
"Everyone puts there their own way of doing things to one side and buys into the same style of play. That's what's so unique about the Lions - everyone puts nationality to one side.
"You've got Welsh fans coming up to English players and saying 'Come on Lions'. That's a unique and amazing feeling to have that support from everybody. The supporters were absolutely amazing and they made you feel really special. It genuinely does give you a boost."
The Lions may have lost the series against the Springboks by the narrowest of margins but there's no doubt that they left their mark in the Republic.
Just like in the first Test against Australia in Brisbane 11 years ago, Britain and Ireland's travelling support seemed to outshine their hosts in both numbers and noise.
"There were so many Lions supporters there," added Ellis, who intends to follow in their footsteps in 2013 or 2017.
"The second Test was just immense, there were so many red shirts compared to green shirts. Speaking to my family who were at the game, the other supporters made them feel so welcome. I felt that as well.
"It's something that I want to follow in the future. I'd love to go on a Lions tour, be a supporter and just get involved. I think it's something you just have to do. I want to go travelling to New Zealand so to follow a tour there would be amazing."