With the game being screened live on BBC 2 the coverage will be linked through to the BBC 1 Children In Need extravaganza for Alex to show how Wales is backing the money raising action.
The Welsh Rugby Union is urging as many supporters as possible to get in on the act by grabbing tickets for the game to be there when the big link up takes place.
With the rugby at centre stage the Children In Need extravaganza will feature a live performance at half time from girl band The Saturdays plus Only Men Aloud.
The musical inserts will be screened on the main BBC 1 output so the Millennium Stadium will be on both BBC 1 and BBC 2 at the same time for match and Children In Need coverage.
Alex Jones who presents The One Show on BBC 1 will be returning to her Welsh roots for the Children In Need event.
She said: "I'm really looking forward to it because I think for one thing that doing Children in Need as a big network production instead of Wales just opting out on TV will show everyone what we're doing.
"And coming to us in the middle of a rugby game - which is typically Welsh and having the Welsh team there in the background - it's a superb idea, it's genius!!
"I used to present theJonathan programme on S4C with Jonathan Davies so I went to all the games then, but my dad's a big rugby fan so he'd always take us as children.
"A Wales match is a social occasion; whether you're a huge rugby fan or not, there is nothing better than the atmosphere at a Wales game - it's just superb.
"And I'm looking forward to seeing the Saturdays. They're kind of the new Girls Aloud, who I love, and I think for some of the men there, it can't get any better than Wales playing Fiji followed by these five absolutely lovely girls singing - it's brilliant.
"I've seen Only Men Aloud quite a lot at different events recently and there is something really fresh about them; they always get the crowd going, and I think they'll really suit the occasion and appeal to the rugby crowd tonight.
"It's going to offer everyone a really great event."
The Wales team are joining in the action by posing for squad pictures wearing the famous Pudsey bobble hats which the team will also wear on arrival at the Stadium and for their traditional warm up.
Tickets are still selling for the Wales v Fiji international priced at just £10 for juniors and £20 for adults so thousands of youngsters will be able to add to the sound volume of support for Children In Need as well as for Wales.
Tickets are available at www.wru.co.uk/ticketsand via telephone 08442 777 888 and at Cardiff Arms Store, at 8 Westgate Street, Cardiff.