The pair first met on the set of 2022 film Christmas in Paradise, and later became romantically involved after Elizabeth reached out to Billy via text last year amid his acrimonious divorce from Firerose. Despite only going public with the relationship in April, the 63-year-old country singer has now made his feelings clear for the British actress.
Taking to social media on Tuesday, Billy - who has been previously married three times - paid tribute to Elizabeth on her 60th birthday.
"Happy birthday to the love of my life," he wrote on Instagram as he added a heart emoji and shared a photo of the happy couple smiling together.
The Achy Breaky Heart hitmaker's daring declaration sparked derision from some social media followers, who questioned how Billy could make such a statement this early in the relationship.
One Instagram user wrote, "How you two just started dating. love of your life what a joke," while another posted, "you just met her."
"How many loves of your life have you had in the last 10 years??" asked a fan.
However, many other followers insisted they were pleased to see the couple together and offered their well wishes.
Elizabeth also made it clear she approved of Billy's comment by posting a series of red heart emojis, while her 23-year-old son Damian Hurley also showed his support for the relationship with a heart emoji.
To mark her milestone birthday, Elizabeth posted a photo of her apparently posing nude in a field as she reflected on recent events in her life.
"Happy birthday to me! This year has already been a wild ride," she wrote on Instagram, as she added: "And... I'm in love."
She signed off saying, "Feeling very blessed and grateful for having the best friends & family in the world ?? pic taken this afternoon... in my birthday suit xxx."
Elizabeth recently discussed the "surprising" reaction to her romance with Billy, but insisted the pair have more in common than people realise.
"It's not surprising to me because we're actually quite similar and get on extremely well," she told Page Six. "We both like to laugh a lot, and we both love the country," she told the outlet. "And we both love country music, both love movies. We've got a lot in common - and cowboy boots, definitely."
