Gavin and Stacey fans only just realising why Neil The Baby sings in the final episode

One of the most heartwarming moments from Gavin and Stacey's grand finale saw a fully-grown Neil the Baby performing a sweet tribute at dad Smithy's wedding - 16 years after mum Nessa welcomed him into the world.

Only now, however, are fans realising why this moment was particularly poignant.

For those who haven't yet sank their teeth into this year's festive special - which also happened to be the last ever episode that the gang will ever film - it followed the events of the 2019 instalment.

Remember, the one where Nessa realised her true feelings, got down on one knee and asked Smithy - who was himself already going out with insufferable girlfriend Sonia - to marry her?

Well, fans were forced to wait five years to discover whether Smithy said 'yes' or 'no' that day.

Naturally, therefore, after the finale kicked off with talk about a wedding, fans hoped Smithy had agreed, only for it to be revealed that Gavin had actually interrupted her proposal, and that he was actually engaged to Sonia instead.

The episode saw the entire cast - including the titular twosome, Pam and Mick, Pete and Dawn, Gwen, Brynn and Jason, and even 'Dave Coaches' - come back to help plan Smithy's big day, even though they all thought his connection with Sonia was one big sham.

Also joining in on the doomed celebrations was actor Oscar Hartland, who played Smithy and Nessa's not-so little boy, Neil 'the Baby'.

Hartland played Neil 'the Baby' as an infant (BBC)

Hartland was cast in the role as an infant, with the pair welcoming Neil during the second series all the way back in 2008.

Fans were shocked back in 2019 to see the child star reprising the role in 2019 for the previous Christmas edition, and even more so to see him again this year - almost a full-grown adult.

When Smithy's wedding to Sonia finally did roll around on Christmas Day, Neil 'the Baby' performed a tear-jerking tribute to his father (played by James Corden), bringing out a guitar and singing The Beatles' 'Blackbird' before the congregation.

The moment left fans in tears, with many unable to comprehend that Smithy was actually marrying someone other than Nessa, and others surprised by the youngster's vocal talents.

It turns out, however, that the inclusion of Neil 'the Baby's' song wasn't just an emotional coincidence, but a conscious choice, being that Hartland is already recognised nationwide for his talent.

That's because the youngster actually appeared on hit TV singing competition The Voice Kids last year.

Hartland performed a song at Smithy's wedding (BBC)

TV critic and broadcaster Scott Bryan told press earlier this week: "Baby Neil, who was actually one of the... babies in Gavin & Stacey when it first debuted, he was in The Voice, and they loved him in The Voice, so that’s why he sings in the film."

A clip from his time on the ITV series saw Hartland telling viewers: "People know me for being Neil the Baby in Gavin & Stacey, which I absolutely love, but now I wanna be known for my music and singing."

Nessa actress Ruth Jones also wished him good luck on the show, telling Hartland in a VT: "We knows what’s occurring, you’re on The Voice Kids. Don’t forget you takes after your mother when it comes to music.

"Go out there and you smash it kid alright? Crackin’."