The former Motley Crue rocker, 51, is more than two decades older than the 30-year-old singer, however he believes that Sofia - to be his fourth wife - is the woman he was destined to settle with.
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"There comes a time in a mans life when you just know your partner is for LIFE!! Say hello to my fiancé and soon to be wife @SOFIofficial," he posted on Monday.
Meanwhile Sofia, addressed her fans on the micro-blogging website in a much more cryptic way.
She joked that that she was now Tommy's fiancée by humorously referencing solo artist Beyoncé Knowles.
"I'm something that rhymes with Beyonce!!!!!" she gushed.
Support for their impending nuptials was followed up by a congratulatory tweet from DJ Deadmau5, who has featured Sofia in his work.
He directed the message at Britney Spears' former backing vocalist – who also goes by stage name SOFI (SomeOtherFemaleInterest) - prompting Tommy to affectionately respond, "Thanks Peaches!!!!"
Tommy has previously been married to model-and-actress Pamela Anderson, actress Heather Locklear and Elaine Bergen (neé Starchuk).
He was engaged to Prince’s former spouse Mayte Garcia for two years but the duo never made it down the aisle.
Tommy reunited with 46-year-old Pamela in 2008 – who she has two children, Branden, 17, and Dylan, 16, with - following their split in 2001. However in January this year the star announced she had remarried her third husband Rick Solomon.
Lately Tommy has been doing the nightclub and music festival rounds with DJ Aero, simultaneously posting about his love on the web for Germany-born Sofia.
He wrote, "Ahhh the day in St.Tropez with my ❤ @SOFIofficial" before sharing a scenic image.