The 38-year-old TV presenter has been dating the pretty blonde for a couple of months now, but until now the happy couple have been keeping quiet about their blossoming relationship.
This week though, Dec broke his silence as he joined his sidekick Ant McPartlin to launch a live arena tour of the hit show, Saturday Night Takeaway.
Dec and Ali pictured together in 2005
Speaking at the unveiling of the tour at London's O2, he told the Sun, "It's going good. Everything's hunky dory.
"It was a little strange because we've had a working relationship for so long. But because it just happened there was no big ta-da.
"Things couldn't be better for me at the moment."
Dec and Ali became close after more than a decade of working together — Ali also manages Ant's career.
A source recently told the newspaper of their romance, "They've adored each other for years and people have often thought they were together — but it's only recently they finally became an item.
"They've kept it quiet for ages but are at last coming to terms with being a couple in public."
Dec has been predominantly single since 2011 when he split from Sky Sports News presenter Georgie Thompson, who recently found love with Olympic sailor Sir Ben Ainslie.
His longest relationship was with TV actress Clare Buckfield; the couple dated for 11 years before parting ways in 2003.