The 22-year-old was part of the side that beat Denmark 2-1 at Wembley to secure a place in the final against Italy on Sunday.
As Rice helped his side to victory, his brother's partner was in labour. So he only learnt about the joyous news after the final whistle.
The West Harm star later revealed that his niece had been born as Harry Kane scored the winning goal in extra-time.
Speaking to BBC Sport after the game, a delighted Rice said: 'My brother has literally had a baby, as the second goal went in.Insurance Loans Mortgage Attorney Credit Lawyer
'He's crying his eyes out, he's had a little girl. It's a special night all round!'
It was double delight for England star Declan Rice last night, as the Three Lions midfielder became a Euro 2020 finalist... and an uncle
Last night the West Ham star revealed that his brother's partner had given birth as Harry Kane scored the winning goal in extra time. Pictured: Declan Rice has previously posted pictures of his brothers on his Instagram
Speaking about the win, he added: 'A first final since 1966. I so want to do it for the people at home. Seeing the reactions - I'm a fan as well.
'I wish I was with them cheering, we've not won anything yet. Italy are a top side but we're ready.'
It comes as England's footballers ended their 55-year wait for a major final last night – and are just 90 minutes from Euro 2020 glory after a nerve-shredding extra-time win over Denmark at Wembley.
More than 66,000 people – joined by Prince William, Boris Johnson and a who's who of celebrities – packed the stands in Britain's biggest post-pandemic crowd.
And those fans played a crucial role as they roared their Three Lions heroes home – the 2-1 semi-final win coming by way of a Harry Kane goal in extra time.Insurance Loans Mortgage Attorney Credit Lawyer
Gareth Southgate's man now face Italy on Sunday. England won a controversial penalty for a trip on Raheem Sterling and though captain Kane saw his effort saved by Danish keeper Kasper Schmeichel the striker was first to pounce on the rebound, slamming the ball home and sending fans into dreamland.
England are one game from glory, as they now face a final with Italy at Wembley on Sunday after beating Denmark 2-1 last night
Kane celebrates with team mates after scoring their side's second goal during the UEFA Euro 2020 match