Trouser-snake has offered to pen and perform a one-off song for Ellen Degeneres and Portia De Rossi's wedding ceremony.

The comedienne-turned-chat show host went public with plans to wed her long-time partner during a taping of her daily show, which aired on Friday.

Timberlake was among the first to congratulate the couple when he appeared on the show minutes later, even offering to sing at the wedding.

Laughing off the suggestion that he should marry his girlfriend, Jessica Biel - and make the event a double wedding, JT offered, "No... but I'll sing at your wedding".

He added: "Write down everything you want to say to Portia and everything you wanna say to Ellen... and I'll put it to music and it'll be amazing".